DM42 Quick Reference Guide

(c) 2019-2025 SwissMicros GmbH, inspired by the HP-42S Quick Reference Guide (c) Copyright 1988 Dex Smith
v3.5.5 (with Free42 3.2.8 Extensions)

Version 2025-04-22
Check http://technical.swissmicros.com/dm42/fat/HELP for updates
Use following link to open the DM42 functions list help file.

Navigation

Press ÷ to move one page backward
Press × to move one page forward
Press - to move one line backward
Press + to move one line forward
Press ▲ to select previous link
Press ▼ to select next link
Press ENTER to jump to selected link
Press EXIT or F1 to exit
Press F2 to jump to Contents
Press F3 to open help file selection dialog

Numpad-like navigation keys

2/8 - single line down/up
3/9 - page down/up
4/6 - prev/next link (same as arrows)
5 - follow the link (same as ENTER)
7 - go to the Contents (same as F2)

Symbols used in this guide

A 123 represents a soft button or anything on the LCD
A STO represents a physical button

Menus
Storage
Data Types
Modes
Executing Functions & Programs
Programming
Using a Variable Menu
The Solver
Numerical Integration
Matrix Operations
Statistics
Base Conversions
HP-42S Functions
Free42 Extensions
HP-41 Function Names
Using the ALPHA Menu
Flags
Virtual variables
F-Buttons
Screenshot
Setup Menu
About

Menus

DM42 calculator has far too many functions to assign a key to each one, so most of them are available in menus rather than directly on keys.
Each menu displays a row of labels at the bottom of the screen, one above each key in the top row of the keyboard.
A function within the menu is activated by pressing the key directly below it. If there are more than six functions in the menu then the ▼▲ annunciator is displayed and the ▼ and ▲ keys allow you to scroll through the menu's pages. There are two kinds of menu:

Application Menu
Function Menu

Application Menu

There are five applications built into the DM42:

BASE Base Conversions
MATRIX Matrix Operations
SOLVER The Solver
STAT Statistics
∫f(x) Numerical Integration

When you enter an application and its menu opens, any other menus are closed automatically. However, you can still open a function menu from within the application and when you've finished with it, it will close and reveal the application menu again.

Function Menu

CATALOG All DM42 Functions
CLEAR Functions for clearing programs and variables
CONVERT Angle, time, and coordinate conversion functions
CUSTOM Displays custom menu
DISP Display Formats
FLAGS Flags
MODES Angles and Coordinates
PGM.FCN Functions useful in programs
PRINT Enable IR Printing
PROB Combinatorics and probability functions

Unlike application menus, a Function menu closes as soon as you have used one of the functions that it contains, with the exception of the CUSTOM menu, which remains open. Should you need to use more than one function from a Function menu, you can instruct the DM42 to keep the menu open by opening it twice in succession.

The Stack

The stack is the scratchpad that you use for performing calculations. It stores and shows you intermediate results as you work through a problem.
The four registers that make up the stack are known as X,Y,Z,T. Auxiliary register LASTx holds contents of X register used in most recent numeric function. Each of these registers can contain data of any type.

Storage Registers

Because of the ephemeral nature of the stack, data in its registers is likely to be lost when a new calculation is started.
More permanent storage can be achieved in the storage registers, of which there are 25 initially, numbered 00 to 24. This number can be altered with the SIZE function in the MODES menu.
STO nn STOres the contents of the X register into the storage register with the given number.
RCL nn ReCaLls the data from storage register nn into the stack.
If SIZE has been used to define more than 100 storage registers then registers numbered 100 and onwards can only be accessed using indirect addressing.
The STATistics application uses some of the storage registers for its internal housekeeping:

R11 Σ x
R12 Σ x²
R13 Σ y
R14 Σ y²
R15 Σ xy
R16 n

If ALLΣ mode is being used (as opposed to LINΣ mode) then the following additional storage registers are used:

R17 Σ ln x
R18 Σ (ln x)²
R19 Σ ln y
R20 Σ (ln y)²
R21 Σ ln x ln y
R22 Σ x ln y
R23 Σ y ln x

The storage registers can be all real numbers or all complex numbers. See Variables for how to switch between the two.

Variables

Rather than referring to stored data by a simple number (the number of the storage register containing it), it is possible to create named variables. Variables allow you to associate a meaningful name with the data. Also, named variables can contain any type of data, not just real or complex numbers.
E.g. suppose you have just calculated the volume of a shape. Store the value currently in the X register representing this volume in a variable named VOL:
STO ENTER VOL ENTER
Variables can have names up to seven characters long.
There is one system-reserved variable, REGS. REGS is a matrix containing the storage registers. REGS can be a real matrix, in which case all of the storage registers, i.e. the elements of REGS, are real numbers, or it can be a complex matrix, in which case all of the storage registers are complex numbers.
To convert REGS (or any other real matrix) to a complex matrix:
0 ENTER COMPLEX STO + REGS
To convert REGS from a complex matrix back into a real matrix:
RCL REGS COMPLEX x<>y STO REGS

The Alpha Register

The alpha Register can store up to 44 characters of text, which equate to two lines of text on the original HP-42S.

Available Memory

The DM42 has about 70KB of system memory that your programs and variables can use. The storage register matrix REGS uses some of this space.
To find out how much memory your DM42 has available, open the CATALOG menu and then press and hold MEM.
If you need more memory then use the CLP (CLear Program) and CLV (CLear Variable) functions from the CLEAR menu to remove unnecessary programs and variables and thus free up additional memory.
DO NOT DELETE THE REGS VARIABLE! Remember, it holds your storage registers! If necessary you can reduce its size with the SIZE command from the MODES menu.

Data Types

Real Numbers
Complex Numbers
Alpha Strings
Matrices
Lists

Real Numbers

Real numbers cover integer and decimal numbers, positive or negative. The range of numbers that the DM42 can handle is approximately 10^-6143 to 10⁶¹⁴⁴ with a precision of 34 digits.

Complex Numbers

A complex number consists of two real numbers associated to form its real part and its imaginary part (rectangular coordinate mode).
Complex numbers are always stored internally in rectangular form but can be displayed directly:
0.2343 i1.4456
or in polar coordinate mode with a magnitude and an angle:
1.4645 ∡80.7937
Both of the examples here represent the same complex number.
To enter a complex number in rectangular mode:
real part ENTER imaginary part COMPLEX
To enter a complex number in polar mode:
Magnitude ENTER angle COMPLEX
The COMPLEX function either combines real numbers (or matrices) in the X and Y stack registers to form a complex number (or matrix) in X, or it performs the opposite operation by splitting the complex number (or matrix) in X into two real numbers (or matrices) in X and Y.
The role of the real number (or matrix) taken from X when combining X and Y or left in X when splitting the complex number (or matrix) in X depends on the display mode, rectangular or polar, in force when COMPLEX is executed. If rectangular then X is/was the imaginary part. If polar then X is/was the angle.
Complex numbers are displayed in polar mode normalised such that the magnitude is always positive and the absolute value of the angle does not exceed 180 degrees.

Alpha Strings

The alpha register contains strings of text up to 44 characters (2 lines on the HP-42S) in length.
Real variables and elements of real matrices (including REGS ) can also contain strings of up to 6 characters in length. Basically, you can store snippets of text anywhere you can store real numbers. However, you cannot store two such snippets in a complex variable.
With Free 42 it's possible to have strings with more than 6 or 44 characters. The related functions are in the function catalog: CATALOG STR.

Matrices

Matrices can be one-dimensional or two-dimensional. A matrix can have any number of rows and columns as long as there is enough memory in the DM42 to store all of its individual elements.
See Matrix Operations for more details.

Lists

Lists are a new data type introduced by Free42, which is an ordered collection of objects of any type, including other lists.
List functions are included with Free42 string functions in the function catalog: CATALOG STR.

Modes

Angles and Coordinates
Other Modes
Display Formats
Printing

Angles and Coordinates

Press MODES
The angle specifiers DEG, RAD and GRAD tell the DM42 to use degrees, radians, and gradians respectively when displaying and interpreting angles.
RECT and POLAR tell the DM42 to display and interpret complex numbers in rectangular and polar mode, respectively.

Other Modes

Press MODES ▼
SIZE resizes the REGS matrix variable, thus defining the number of storage registers you can use.
QUIET switches off the internal buzzer and keeps the DM42 nice and.... quiet!
CPXRES allows the DM42 to return complex results when working on real numbers (e.g. square root of a negative number) while REALRES ensures that only real numbers are returned. In this case, operations that would otherwise return a complex result trigger an Invalid Data error. Operations given a complex number as an argument will return a complex number regardless of the CPXRES/REALRES setting.
KEYASN means that variables and programs assigned to the CUSTOM menu with the ASSIGN command will be shown in the CUSTOM menu. If LCLBL is selected then local alpha labels populate the CUSTOM menu.

Display Formats

Press DISP
FIX, SCI and ENG instruct the DM42 to display real numbers in fixed decimal, scientific and engineering notation, respectively, with a set number of decimals.
When ALL is selected, numbers are displayed with up to 12 digits precision, which was the native precision of the HP-42S.
Depending on where in the world you are, you will be used to using a dot as the decimal separator and a comma for grouping digits three by three before the decimal (e.g. 1,234.56 ) or, as in most of Europe, a comma as the decimal separator and a dot for grouping digits before the decimal (e.g. 1.234,56 ). RDX. selects the dot as the decimal separator and RDX, selects the comma.

Printing

Press PRINT ▲
PRON and PROFF enable and disable printing by setting or clearing respectively flags 21 and 55.
MAN leads to items being printed manually. NORM leads to input and calculation results alone being printed automatically while TRACE sends a trace of all operations to the printer.
Additional modes are described under "Matrix Operations" and "Statistics."

Executing Functions & Programs

Quick access to programs and functions
Addressing modes

Any function or program can be executed by pressing XEQ and entering its name. If there is more than one program with the same name then when you attempt to XEQ that program, the one closest to the permanent .END. marker will be executed.
Only the current program will be searched if the name that you give is that of a local label.

Quick access to programs and functions

There are four ways to get at your programs and at the DM42's functions quickly:

You can ASSIGN up to 18 names of programs or variables to the CUSTOM menu. Pressing an item in the CUSTOM menu is the same as executing it (XEQ ) if it's a program or built in function or, if it is a variable, recalling it (RCL ).
When you press the XEQ button, the program catalog is automatically presented to you. Simply scroll through the catalog with the ▲ and ▼ keys if needed and select the program to run.
The Run/Stop Key R/S starts running the current program at the current line or stops a running program once the instruction that it is working on has completed.
All of the built in functions of the DM42 are available in the Function Catalog that can be opened by pressing CATALOG FCN

Addressing modes

Some functions require a parameter that tells them on what specific item to operate. These functions accept one or more of the following addressing modes:

Numeric: these functions include RCL, SF, GTO, and others. They prompt you to enter a numerical value by displaying an underscore for each digit that they are expecting. For example, if you press SIZE, the DM42 displays
SIZE ____
prompting you to input four digits. You can always input fewer digits and terminate the input with ENTER and the DM42 will assume that the missing digits are zeroes on the left.
Alpha: some functions that accept numeric addressing also accept alpha addressing. An example of one such function is RCL, which allows you to specify the number of a storage register to recall or the (alpha) name of a variable. In many cases, the DM42 will show you a menu of alpha names that are valid for the instruction that you are typing but if not, you can always use the ALPHA menu to type it in yourself.
Stack: because the stack registers can hold anything that a storage register can, they can also be used in place of a storage register. For example, to recall the contents of the T register into X (trick to roll the stack upwards instead of downwards), do the following:
RCL . ST T
Indirect Addressing: this is a technique that does not give the DM42 the parameter that it needs. Instead, it tells the DM42 where to find that parameter. For example, to execute the program whose name is stored in storage register 24, you would: XEQ . 24
Stack registers can also be used with indirect addressing. For example, suppose that the name of the program that you want to execute is not in R24 but in the X register of the stack. In this case you would:
XEQ . . ST X

Programming

Program-Entry
Labels
The Do-lf-True Rule
Looping

Program-Entry

PRGM enters or exits Program-entry mode
GTO . . moves to a new program space
GTO . nnnn moves to line number nnnn
← deletes the current program line
SST moves to the next program line*
BST moves to the previous pgm line*

* Use ▲ or ▼ if no menu is displayed.

Labels

A program label is simply a marker used to identify a program or a routine within a program.
Global labels can be accessed from anywhere in memory (and therefore should be unique). Global labels are distinguished from local labels by quotation marks (such as LBL "SAMPLE" ).
Local labels can be accessed only within the current program (and should be unique within the current program). There are two types of local labels:

Numeric (LBL 00 - LBL 99)
Alpha (LBL A - LBL J and LBL a - LBL e )

The Do-lf-True Rule

The do-if-true rule determines how program lines are executed when a conditional function is encountered. If the condition is "true," the line immediately following the conditional is executed. If the condition is "false," the line following the conditional is skipped.

Looping

The ISG and DSE functions control looping. Each accesses a variable or register containing a control number in the form ccccccc.fffii; where ccccccc is the current counter value, and fff is the ﬁnal counter value, and ii is the increment size (default is 1). Both ISG and DSE follow a variation of the do-if-true rule: if the count is not complete, the line following the instruction is executed (usually a branch to the top of the loop).
For example, this program segment counts from 1 to 52 by threes (executing the loop 18 times) and then beeps.
17 1.05203
18 STO "COUNT"
19 LBL 01
…
23 ISG "COUNT"
24 GTO 01
25 BEEP

Using a Variable Menu

A variable menu may be displayed by the Solver or Integration applications, or by the VARMENU function within a program. Each label in the menu represents a variable. While the menu is displayed, you can:

Store a value into a variable:
Key in the value and then press the menu key.
Recall the contents of a variable:
Press RCL and then the menu key.
View the contents of a variable without recalling it:
Press (shift) and then hold the menu key down.
Select a variable:
Press the menu key without keying in a number first. This action places the variable name in the alpha register and continues execution.
(For the Solver, this is how you select the unknown variable. For Integration, this is how you select the variable of integration.)

You can select and use any function menu without exiting from the variable menu.

The Solver

The Solver is a root finder that allows you to solve for an unknown variable in an expression, given values for all the other variables. Expressions are written as programs. There are three parts to a Solver program:

The program must begin with a global label.
Immediately following the global label, menu variables are declared with MVAR instructions.
Finally, the body of the program should evaluate the expression. Recall the variables as they are needed and calculate f(x) (where f(x) = 0 for your expression of one or many variables).

After entering the program, these are the steps for using the Solver:

Press SOLVER
Select a Solver pgm from the menu.
Use the variable menu to store a value into each of the known variables. Optional: store one or two guesses into the unknown variable to direct the Solver to a solution.
Solve for the unknown variable by pressing the corresponding menu key.

A Simple Example: For the expression A + B = C, rewrite the expression as A + B - C = 0. The Solver program looks like this:

01 LBL "SIMPLE"
02 MVAR "A"
03 MVAR "B"
04 MVAR "C"
05 RCL "A"
06 RCL+ "B"
07 RCL- "C"
08 END

Hint: create the variables before entering the program. After entering the program, you can use it to solve for any variable, given a value for each of the others. For example, find A when B = 12 and C = log(B).

Select the program: SOLVER SIMPL
Store B: 12 B
Store C: LOG C
Solve for A: A

Numerical Integration

The Numeric Integration application allows you to calculate an approximation of a definite integral. The integrand, f(x), is written as a program similar to a Solver program (see The Solver ). That is, the program must use a global label, declare the menu variables, and evaluate f(x).

After entering the integrand program, here are the steps for using the Integration application:

Press ∫f(x)
Select an integrand program from the menu.
Use the variable menu to store a value into each of the variables that should remain constant.
Select the variable of integration by pressing the corresponding menu key.
Store the lower limit (LLIM ), the upper limit (ULIM ), and the accuracy factor (ACC ).
Press ∫ to calculate the integral. The approximation for the integral is returned to the X-register and the uncertainty of computation is returned to the Y-register.

Matrix Operations

To create a new m × n matrix, enter the dimensions:
m ENTER n (for m rows and n columns) and then press:
MATRIX NEW for a matrix in the X-register.
Or MATRIX ▼ DIM ENTER name ENTER for a matrix in a variable. If the matrix already exists, the DIM function redimensions it.

Edit the matrix in the X-register:
MATRIX EDIT

Edit a named matrix:
MATRIX ▼ EDITN name

When a matrix is being edited it is said to be indexed. (To index a named matrix without editing it, use the INDEX function.) Whenever there’s an indexed matrix, two pointers are used to indicate the row and column of the current element: I and J, respectively.

Wrap and Grow Modes. If the index pointers are positioned to the last (lower-right) element in a matrix and you move to the right one position:

The pointers wrap around to the first element of the matrix (Wrap mode).
Or, the matrix grows by one complete row and the pointers move to the new row (Grow mode).

Wrap mode is automatically selected whenever you enter or exit the matrix editor. (The WRAP and GROW functions are in the second row of the editor menu.)

Matrix Arithmetic. Most arithmetic and other operations work for matrices just as for individual numbers. Anytime a matrix is used in a mathematical operation with a complex number, the result is a complex matrix. Therefore, you can make any matrix complex by adding 0 + i0 to it:
0 ENTER COMPLEX +
or 0 ENTER COMPLEX STOM + name

To solve a system of simultaneous linear equations represented by the matrix equation AX = B:

Press MATRIX SIMQ.
Key in the number of unknowns. The calculator automatically creates or redimensions the matrix variables MATA, MATB, and MATX.
Optional: If your equations involve complex numbers, make MATA and/or MATB complex (as shown at the top of this page).
Press MATA , fill the matrix and press EXIT
Press MATB , fill the matrix and press EXIT
Press MATX to calculate the solution matrix. Use the matrix editor keys to view the results.

Statistics

Statistical data is accumulated into 6 or 13 sequential storage registers. Initially, the first summation register is R11. Use the ΣREG function to change the location of the first summation register. ΣREG does not move the data in the registers.

Options to set the summation mode:

STAT ▼ ALLΣ to use all 13 coefficients
STAT ▼ LINΣ to use only the first six coefficients (which allows only linear curve fitting)

Clear the summation registers:
CLEAR CLΣ

Options to accumulate data:

For each x-y data pair: y-value ENTER x-value Σ+
For each single-point data value: x-value Σ+
For x-y data pairs stored in a two-column matrix (x-values in column 1; y-values in column 2): Place the matrix in the X-register and then press Σ+

To undo mistakes:
Put the incorrect data in the stack (try LASTx ).
Press Σ- and continue accumulating data.

To select a curve model for forecasting:
Press STAT CFIT MODL
and then one of the following:

LINF linear model: y = mx + b
LOGF logarithmic model: y = m ln(x) + b
EXPF exponential model: ln(y) = mx + ln(b)
PWRF power model: ln(y) = m ln(x) + ln(b)
BEST selects the model that returns the best correlation coefficient

Base Conversions

Real numbers are displayed according to the current base mode (Hexadecimal, Decimal, Octal, or Binary). You can change the base mode using the BASE menu or by manually executing HEXM, DECM, OCTM, or BINM. Decimal mode is automatically selected when you exit from the BASE menu.
By default integer numbers have a 36-bit size as on the HP-42S. With the WSIZE function this size can be set from 1 to 64 bits.
Press and hold SHOW to display:

A hexadecimal or decimal number in full-precision decimal form.
An octal number in octal form.
All the bits of a binary number of 44-bits or less.
Or a binary number with more than 44-bits in hexadecimal form.

When the BASE menu is displayed, the following keys are temporarily redefined with these integer functions:

+/- BASE+/-	2’s complement.
÷ BASE÷	integer divide.
× BASE×	integer multiply.
- BASE-	integer subtract.
+ BASE+	integer add.

Bits are numbered from right to left beginning with 0. Bit 35 (or the most significant bit depending on WSIZE) is the sign bit. Negative numbers are represented in 2’s complement form. Nondecimal numbers longer than WSIZE are displayed as <Too Big>

HP-42S Functions

Under CATALOG FCN):

A B C D E F
G H I J K L
M N O P Q R
S T U V W X Y
Test Functions
1+- Σ → Matrix Pointers %
Hidden Matrix Functions


A
ABS		Absolute value
ACOS		Arc cosine
ACOSH		Arc hyperbolic cosine
ADV		Advance paper
AGRAPH	Alpha graphics
AIP		Alpha integer part
ALENG		Alpha length
ALL		All display format
ALLΣ		ALLΣ mode (13 sum regs)
AND		Logical AND
AOFF		Alpha off
AON		Alpha on
ARCL		Alpha recall
AROT		Alpha rotate
ASHF		Alpha shift
ASIN		Arc sine
ASINH		Arc hyperbolic sine
ASSIGN	Assign CUSTOM menu key
ASTO		Alpha store
ATAN		Arc tangent
ATANH	Arc hyperbolic tangent
ATOX		Alpha to X
AVIEW		Alpha view

B
BASE+		Base add
BASE-		Base subtract
BASE×		Base multiply
BASE÷		Base divide
BASE+/-	Base change sign (2’s compl.)
BEEP		Beep
BEST		Best ﬁt model
BINM		Binary mode
BIT?		Bit test (x-th bit of y)
BST		Back step

C
CF			Clear ﬂag
CLA		Clear alpha register
CLALL		Clear all memory
CLD		Clear display
CLKEYS	Clear CUSTOM menu keys
CLLCD		Clear LCD
CLMENU	Clear programmable menu
CLP		Clear program
CLRG		Clear registers
CLST		Clear stack
CLV		Clear variable
CLX		Clear X-register
CLΣ		Clear summation registers
COMB		Combinations
COMPLEX	Complex
CORR		Correlation
COS		Cosine
COSH		Hyperbolic cosine
CPXRES	Complex-result enable
CPX?		Complex test
CROSS	Cross product
CUSTOM	CUSTOM menu

D
DECM		Decimal mode
DEG		Degrees mode
DEL		Delete program lines
DELAY	Printer delay time
DELR		Delete matrix row
DET		Determinant
DIM		Dimension matrix
DIM?		Dimensions of matrix in X
DOT		Dot product
DSE		Decrement, skip if ≤ zero

E
EDIT		Edit matrix in X-register
EDITN		Edit named matrix
END		End of a program
ENG		Engineering display format
ENTER	Enter
EXITALL	Exit all menus
EXPF		Curve-fitting model: exp.
E↑X		Natural exponential
E↑X-1		Nat. exp values near zero

F
FCSTX	Forecast x given y (stat)
FCSTY	Forecast y given x (stat)
FIX		Fixed dec. display format
FRNM		Frobenius norm of X matrix
FP			Return fractional part

G
GAMMA		Gamma function
GETKEY	Put next key number to X-reg
GETM		Get matrix
GRAD		Grads angular mode
GROW		Grow mode (matrix edition)
GOTO		Go to label

H
HEXM		Hexadecimal mode
HMS+		Add x and y using H.MMSSss
HMS-		Subtract x from y H.MMSSss

I
I+			Inc. row pointer (matrix)
I-			Dec. row pointer (matrix)
INDEX		Index matrix
INPUT		User input (prog. only)
INSR		Insert row (matrix edition)
INTEG		Integrate
INVRT	Invert matrix in X-register
IP			Return integer part
ISG		Increment, skip if greater

J
J+			Inc. column pointer (matrix)
J-			Dec. column pointer (matrix)

K
KEYASN	Key-assignments mode
KEYG		On key, go to
KEYX		On key, execute

L
LASTX	Last x
LBL		Label
LCLBL		Local label mode
LINF		Linear ﬁt model
LINE		Linear mode (six sum regs)
LIST		List program lines
LN			Natural logarithm
LN1+X		Nat log for values near zero
LOG		Common logarithm
LOGF		Logarithmic ﬁt

M
MAN		Manual printing
MAT?		Matrix test
MEAN		Arithmetic mean (average)
MENU		Programmable MENU
MOD		Modulo
MVAR		Menu variable

N
N!			Factorial
NEWMAT	New matrix
NORM		Normal printing
NOT		Logical NOT

O
OCTM		Octal mode
OFF		Off
OLD		Old element value
ON			Continuous on
OR			Logical OR

P
PERM		Permutations
PGMINT	Program to integrate
PGMSLV	Program to solve
PI			pi
PIXEL		Pixel on
POLAR	Polar mode
POSA		Position in alpha
PRA		Print alpha
PRLCD	Print LCD
PROFF	Printing off
PROMPT	Prompt
PRON		Printing on
PR?		Print program
PRSTK	Print stack
PRUSR	Print user vars and labels
PRV		Print variable
PRX		Print X-register
PR2		Print summation registers
PSE		Pause
PUTM		Put matrix
PWRF		Power ﬁt

Q
QUIET		Quiet mode

R
RAD		Radians mode
RAN		Random number
RCL		Recall
RCL+		Recall add
RCL-		Recall subtract
RCL×		Recall multiply
RCL÷		Recall divide
RCLEL	Recall element
RCLIJ		Recall IJ pointers
RDX,		Radix comma
RDX.		Radix period
REALRES	Real-results only
REAL?		Real test
RECT		Rectangular mode
RND		Round
RNRM		Row norm
ROTXY	Rotate y by x bits
RSUM		Row sum
RTN		Return
R<>R		Row swap row
R↑			Roll up
R↓			Roll down

S
SCI		Scientiﬁc notation
SDEV		Standard deviation
SEED		Seed (for RAN)
SF			Set ﬂag
SIGN		Sign
SIN		Sine
SINH		Hyperbolic sine
SIZE		Size of REGS
SLOPE		Slope
SOLVE		Solve for variable
SQRT		Square root
SST		Single step
STO		Store
STO+		Store add
STO-		Store subtract
STO×		Store multiply
STO÷		Store divide
STOEL	Store element
STOIJ		Store IJ pointers
STOP		Stop program
STR?		String test
SUM		Recall Σx and Σy

T
TAN		Tangent
TANH		Hyperbolic tangent
TONE		Tone (0-9)
TRACE	Trace printing
TRANS	Transpose matrix

U
UVEC		Unit vector

V
VARMENU	Variable menu
VIEW		View

W
WMEAN	Weighted mean
WRAP		Wrap mode

X
X<>		x exchange
X<>Y		x exchange y
XEQ		Execute
XOR		Exclusive OR
XTOA		X to alpha
X²			Square, x²

Y
YINT		Y-intercept
Y^X			Power, y^x

1-+
1/X		Reciprocal
10^X		Common exponential, 10x
+			Add
-			Subtract
×			Multiply
÷			Divide
+/-		Change sign
%			Percent
%CH		Percent change

Summation
Σ+			Summation plus
Σ-			Summation minus
ΣREG		Set loc. of 1st sum reg
ΣREG?		Recall loc. of 1st sum reg

→ Conversions
→DEC		To decimal.
→DEG		To degrees.
→HMS		To hours-minutes-seconds.
→HR		To decimal hours.
→OCT		To octal.
→POL		To polar.
→RAD		To radians.
→REC		To rectangular.

Matrix Pointers
←			Index pointers left.
↑			Index pointers up
↓			Index pointers down
→			Index pointers right

Percentage
%			Percent
%CH		Percent change

Hidden Matrix Functions
These functions hidden in the HP-42s are at the end of the DM42 catalog:
[MIN]		Gets a column smallest element
[MAX]		Gets a column largest element
[FIND]	Searches a matrix for a given element

Test Functions

If true, execute the next program line. If false, skip the next program line.

X<0?	less than zero
X<Y?	less than y
X≤0?	less than or equal to zero
X≤Y?	less than or equal to y
X=0?	equal to zero
X=Y?	equal to y
X≠0?	not equal to zero
X≠Y?	not equal to y
X>0?	greater than zero
X>Y?	greater than y
X≥0?	greater than or equal to zero
X≥Y?	greater than or equal to y

Free42 Extensions

The Free42 Extensions can be found in the second and third rows of the CATALOG: CATALOG ▼. They are grouped in several sub-catalogs, which correspond with the sections below.

TIME Time and Date Functions
XFCN Extended Functions
BASE BASE Enhancements
PRGM Programming Utilities
STR String and List Functions
STK Stack
MISC Other Extensions

A few functions are not in the CATALOG and need to be accessed by their name with XEQ name or ASSIGN name:

Not in CATALOG

Time and Date Functions
ADATE	Appends the contents of the X register to the ALPHA register, formatted as a date value.
ATIME		Appends the contents of the X register to the ALPHA register, formatted as a time value.
ATIME24	Like ATIME, except it always formats the time in 24-hour format.
CLK12		FDisplay the time in 12-hour format with AM/PM.
CLK24	Display the time in 24-hour format.
DATE		Returns the current date to the X register.
DATE+	Takes a date from Y, and adds a number of days from X.
DDAYS	Number of days between the dates in Y and in X.
DMY		Set the date format to day/month/year.
DOW		Calculates the day of the week for the date in X. (Sunday=0; Monday=1; etc)
MDY		Set the date format to month/day/year.
TIME		Returns the current time in X in 24-hour format.
YMD		Set the date format to year/month/day.

Extended Functions
ANUM		Scans the ALPHA register for a number, and places it into X.
RCLFLAG	Gets the state of all flags and returns them as a complex number.
STOFLAG	Restores the state of all flags that were retrieved using a previous RCLFLAG.
X<>F		Exchanges flags 0-7 with the X register.

BASE Enhancements
A...F	Sets HEXM mode and activates the A...F menu.
BRESET	Resets all BASE modes back to the HP-42S defaults: WSIZE 36, signed, not wrapped.
BSIGNED	Toggles signed mode.
BWRAP	Toggles wrapped mode.
WSIZE	Sets the word size to the number in X, between 1 and 64.
WSIZE?	Returns the current word size.

Programming Utilities
CPXMAT?	Tests whether the object in the X register is a complex matrix.
CSLD?	Tests whether the 'stack lift disable' flag (30) was set when the latest XEQ was performed.
ERRMSG	Returns the error message for the most recent error to be caught using flag 25.
ERRNO	Returns the error number for the most recent error to be caught using flag 25.
FUNC		Save the contents of the stack and LASTx, and restore then when the function returns, according to the parameter.
GETKEY1		Like GETKEY, except it does not halt program execution when EXIT or Shift-EXIT are pressed.
GETKEYA		Like GETKEY, except it does not wait for a keystroke if the keyboard buffer is empty, returns 0 immediately in that case.
GETLI		Direct matrix access: expect an index in X; pushes the indexed item onto the stack. See PUTLI.
GETMI		Direct matrix access: expects a row index in Y and a column index in X; pushes the indexed item onto the stack. See PUTMI.
LSTO		Creates local variables that exist only for the duration of the current subroutine, and are automatically deleted when it returns.
LASTO	Relates to LSTO like ASTO relates to STO.
LCLV		CLV for local variables. LCLV only deletes local variables that were created at the current RTN level.
NOP		No Operation, encoded as 0xF0, which corresponds to TEXT 0 in the HP-41.
PGMMENU	Presents a menu of all global labels that have MVAR instructions
PGMVAR	Prints all the variables associated with the given LBL through MVAR declarations.
PUTLI		Direct matrix access: expects an index in Y and an item in X, and stores the item at the specified index. See GETLI.
PUTMI		Direct matrix access: expects a row index in Z, a column index in Y, and an item in X, and stores the item at the specified indices. See GETMI.
RTNERR	Return Error from a function.
RTNNO	Return from conditional function, RTNNO causes the line after the calling XEQ to be skipped.
RTNYES	Return from conditional function, return to the line after the calling XEQ.
SKIP		Skips the next line, like a test that always tests false.
SST↑		Step Out: Starts program execution, continuing until just after the end of the current function.
SST→		Step Over: Executes one line of code, and if that line is a function call, it is executed in that one step.
SST↓		Step Into: Executes one line of code, alias for the original SST function. Not in CATALOG.
TYPE?	Returns an integer, representing the type of the object in the X register. 1: Real Number, 2: Complex Number, 3: Real Matrix, 4: Complex Matrix, 5: String, 6: List
VARMENU1		Modified version of VARMENU.
X=? X≠? X<? X>? X≤? X≥?	Compare X to any register or variable.
0=? 0≠? 0<? 0>? 0≤? 0≥?	Compare any register or variable to 0.

String and List Functions
These string functions introduced by Free42 work with unlimited-length strings, on the stack. (see XSTR for creating such strings)
APPEND	Adds the object in X to the string or list in Y. If Y is a string, the contents of X will be converted to a string. If X is a list, it will be added to Y as one element.
C→N		Convert character to number.
EXTEND	Adds the object in X to the string or list in Y. If Y is a string, the contents of X will be converted to a string. If X is a list, it will be added to Y element by element.
HEAD		Removes and returns the first character or element from the string or list named by the function's parameter.
LENGHT	Returns the length of the string or list in X.
→LIST	Creates a list from objects on the stack. The number of objects is taken from the X register.
LIST→	Performs the inverse of the →LIST operation.
LIST?		Tests whether the object in X is a list.
LXASTO	Like LASTO, but the entire ALPHA register, not just the first 6 characters.
NEWLIST	Returns a new empty list.
N→C		Convert number to character.
N→S		Convert number to string.
NN→S		Like N→S, but works as if it's always in ALL mode.
POS		Finds the first occurrence of the string/list X in Y. Or of the string/list X in Z starting from Y.
REV		Reverse the string or list in X.
SUBSTR	From the string/list in Z, gets the substring/sublist starting at index Y and ending just before index X.
S→N		Convert string to number.
XASTO	Like ASTO, but the entire ALPHA register, not just the first 6 characters.
XSTR		Create a string directly in the X register, without needing the ALPHA register and without the six-character limit of ASTO.
XVIEW	This function works just like AVIEW, except it takes the text from the X register rather than the ALPHA register, so it doesn't have the 44-character length restriction of AVIEW.

Stack
The big stack functions are enabled only if the option "Dynamic Stack Extension" is checked in Setup → Settings.
4STK		4-level Stack. Turns off big stack mode, returning to the TZYX stack.
DEPTH	Returns the current stack depth.
DROP		Drops level 1. In 4-level mode, the stack is replenished with zeroes from the top.
DROPN n	Drops levels 1..n. In 4-level mode, the stack is replenished with zeroes from the top.
DUP		Duplicates level 1.
DUPN n	Duplicates levels 1..n. In 4-level mode, n must be 2 or less.
L4STK	Local 4-level Stack, automatically restore the previous stack mode when the current function returns.
LNSTK	Local N-level Stack, automatically restore the previous stack mode when the current function returns.
NSTK		N-level Stack. Turns on big stack mode.
PICK n	Gets the object from level n.
R↑N n		Rolls up levels 1..n. R↑ is equivalent to R↑N depth.
R↓N n		Rolls down levels 1..n. R↓ is equivalent to R↓N depth.
UNPICK n	Puts an object into level n. Consumes the contents of level 1, unlike STO, and n refers to the stack level number after X has been dropped.

Other Extensions
A2LINE	Create program lines containing the current contents of the ALPHA register, to be set.
A2+LINE	Create program lines containing the current contents of the ALPHA register, to be appended.
C.LN1+X	Complex-capable version of LN1+X.
C.E↑X-1	Complex-capable version of E↑X-1.
CAPS		NOP on the DM42 which is always in Mixed mode.
FMA		Fused Multiply-Add. Calculates Z*Y+X using the DM42's native FMA function.
IDENT		Returns the version of Free42 core used in aabbccdd format, with 3.1.12b being formatted as 3011202.
LOCK, UNLOCK		Protect/Unprotect current program against editing. Program pointer arrow is gray when locked. Must be executed in PRGM mode. Affect only the current program.
Mixed	NOP on the DM42 which is always in Mixed mode.
PCOMPLEX	Works like COMPLEX, but always in polar mode.
RCOMPLEX	Works like COMPLEX, but always in rectangular mode.
PRREG	Prints the numbered registers. Also located in PRINT menu.
STRACE	Stack Trace mode. Variation on TRACE mode, printing the entire stack instead of just X.
X2LINE	Create program lines containing the current contents of the X register, to be set.
WIDTH HEIGHT	Get the display size, in pixels. The main use of these functions is to make programs that use PIXEL and AGRAPH resolution-independent.
Not in CATALOG
SST↓		Step Into: Executes one line of code, alias for the original SST function.

HP41 Function Names

Some function names used in the DM42 are different from those on the HP-41, even though they work identically.
The HP-41 function names do not appear in the function catalog, when executed they are automatically converted to the corresponding DM42 function.

HP-41		DM42
CHS		+/-
DEG		→DEG
D-R		→RAD
ENTER↑	ENTER
FACT		N!
FRC		FP
HMS		→HMS
HR			→HR
INT		IP
OCT		→OCT
P-R		→REC
RDN		R↓
R-D		→DEG
R-P		→POL
ST+		STO+
ST-		STO-
ST*		STO×
ST/		STO÷
X<=0?		X≤0?
X<=Y?		X≤Y?
*			×
/			÷

Using the ALPHA Menu

To type an alpha string into the alpha register:

Press ALPHA to select the ALPHA menu.
Optional: press ENTER to turn on the cursor (in Program-entry mode, inserts the I- symbol).
Type the string using the characters shown below. Use shift to type lowercase letters.
Press EXIT or ENTER

Flags

00-10 User Flags
11 Auto Execute
12 Print Double-wide
13 Print Lowercase
15-16 Print Mode
19-20 General Use
21 Printer Enable
22 Numeric Input
23 Alpha Input
24 Ignore Range Errors
25 Ignore Next Error
26 Beeper Enable
27 CUSTOM Menu
28 Radix Mark Period
29 Digit Separators
30 Stack Lift Disable
31 DMY Date Format
34-35 AGRAPH Control
36-39 Number of Digits
40-41 Display Format
42 Grads Mode
43 Radians Mode
44 Continuous On
45 Solving
46 Integrating
47 Variable Menu
48 Alpha Mode
49 Low Battery Power
50 Message
51 Two-Line Message
52 Program-Entry Mode
53 INPUT
55 Printer Existence
56 Linear Model
57 Logarithmic Model
58 Exponential Model
59 Power Model
60 AllΣ Mode
61 Log Model Invalid
62 Exp Model Invalid
63 Pwr Model Invalid
64 Shift State
65 Matrix Editor In Use
66 Grow Mode
67 YMD Date Format
68-71 Base Mode
72 Local-Label Mode
73 Polar Mode
74 Real-Result Only
75 MENU
76 Edge Wrap
77 End Wrap
78 Base Signed
79 Base Wrap
80 Big Stack mode
81-99 User Flags

Flags 0-10 are indicated by annunciators at the top of the display.
Flags 36-80 are read-only and cannot be altered with SF, CF, FS?C, or FC?C.

Virtual variables

The concept of "Virtual Variables" is used to manage some of the new features specific to the DM42 calculator. These are variables that do not (and cannot, for that matter) exist in the DM42's variable table, but are used to read or change state variables specific to DM42.

DevID	(read-only) Hardware Device ID
RefLCD	(read-write) Refresh Zones 0 = None 1 = Main area 2 = Goose 3 = Main area and goose 4 = Annunciators 5 = Annunciators and main area 6 = Annunciators and goose 7 = Everything
GrMod	(read-write) Graphics Modes 0 = HP-42S resolution 131x16 1 = reserved (maps to 0) 2 = DM42 half resolution 200x120 3 = DM42 full resolution 400x240
ResX	(read-only) X-resolution for current graphics mode set in GrMod
ResY	(read-only) Y-resolution for current graphics mode set in GrMod
Vbat	(read-only) battery voltage

F-Buttons

The top row consists of six unprinted buttons referenced as F-Buttons (F1-F6) or soft-menu buttons.

F1 Displays this Help
F2 Toggle the system soft menu visibility
F3 In Help mode, open help file selection dialog
F4 Increase buzzer volume
Shift-F4 Decrease buzzer volume
F5 Toggle stack alignment (Left, Right, Right Underlined)
Shift-F5 Toggle between sans and HP font
F6 Increase font size
Shift-F6 Decrease font size

Note that font changes using F5/F6 affect displaying of calculator stack and font in program mode and are stored independently for both stack and program mode.

Screenshot

Pressing SHIFT and DISP simultaneously makes a screenshot and saves a BMP graphics file in the folder /SCREENS.
The file name is made up by the current date and time.

Setup Menu

File
Calculator State
Print_To_File
Settings
System
About

Setup Menu → File

Save and Load DM42 Programs to FAT Disk as *.raw files.

Load Program
Select RAW file and load in DM42 memory
Save Program
Select one or more DM42 programs from memory and save as one RAW file
Activate USB Disk
Prepare DM42 for connection with computer for file exchange
Show Disk Info
Display FAT Disk information

Setup Menu → Calculator State

The complete calculator state can be saved and loaded as one file (*.f42).

Load State
Load previously saved calculator state
Save State
Save current calculator state as a file
Load Clean State
Load default settings

Setup Menu → Print To File

Graphics Print
Selecting this menu item enables printing to graphics file.
Text Print
Selecting this menu item enables printing to text file.
Graphics in Text
Selecting this menu item enables to see graphics in text file.
Don't print to IR
Selecting this menu item disables default printing to IR printer.

Setup Menu → Settings

Set Time
Set time and select 12h/24h format
Set Date
Set date and select MDY/DMY format
Status Bar
Display State Filename
Display Day of Week
Display Date
Select a Date Separator of . - /
Display Month Shortcut as 3 letter abrv.
Display Time
Display Power Voltage in Header
Stack Font Sizes
Allows to set font size offsets for registers X, Y, Z, T, L and A
Beep Mute
Mute beep in all cases.
Slow Auto-repeat
This option makes auto-repeat of pressed and held buttons slower.
Stack Layout
These are the options:
XYZTL
XYZTA
XYZL
XYZA
XY
LXYZT
Dynamic Stack Extension
This option enables or disables the 'Big Stack' extension of Free42

Setup Menu → System

Warning: Certain actions in this menu can destroy all stored data of the calculator.
Please run 'Save Calculator State' in 'File' menu first to preserve data over potential RESET.

Flashing firmware from FAT
Starts flashing of new firmware if firmware file is copied to root of FAT filesystem.
Bootloader
Connect USB to enter bootloader mode. Note that reset is the only way to exit bootloader mode.
Program Info
Displays info about currently loaded program
Reset to DMCP menu
Resets calculator and enters DMCP menu
Format FAT Disk
This will format FAT filesystem. All data will be erased!
FAT Disk Media Test
All data stored in the FAT disk will be destroyed by this low-level media test!
Power OFF mode
Allows to set power OFF mode. Only for diagnostics.
Self Test
Set of tests for KBD, LCD, IR, BEEP and Diagnostics

About

DM Calculator Platform
(C) 2014-2025, SwissMicros GmbH
Free42
(C) 2004-2025, Thomas Okken
Intel Decimal Floating-Point Lib
(C) 2007-2018, Intel Corp.
DM42 Quick Reference Guide
based on HP-42S Quick Reference Guide (c) Copyright 1988 Dex Smith
Thanks to user Nagash_X for helpful contribution.

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