PX-42F-Plus User Manual

The PX-42F-Plus runs Plus42, an enhanced HP-42S, on the PX-42F calculator. This manual covers what the calculator adds around Plus42: how the screen is laid out, which font is used when, every option in the settings menu, and the commands it adds. For the calculator's functions themselves (the stack, programming, the solver, matrices, units, equations), see the Plus42 and HP-42S documentation.

1. Special keys

These key combinations belong to the PX-42F-Plus itself. They work on the calculator screen, and the last three in the settings menu too.

The calculator also turns itself off after the Sleep Timer, and when the battery runs empty (about 3.45 V).

Typing in ALPHA

While you type text in ALPHA, the keyboard has three modes, as on the DM42. The status bar shows which one is on: [ ], [a] or [A]. Press ALPHA (SHIFT then ENTER) while in ALPHA for the next mode. To leave ALPHA, press EXIT. The calculator remembers the last mode, also after it is turned off, and the next ALPHA starts in it. The first time, ALPHA starts in [ ].

In program mode, hold SHIFT down and press ↑ or ↓ for BST or SST while typing text. Hold ↑ down to keep stepping back.

2. The screen

The screen is 250 × 122 pixels. From top to bottom it has three parts:

1. The status bar: a black bar 12 pixels tall. See The status bar.
2. The lines: the stack, messages, programs, the equation editor, whatever Plus42 is showing.
3. The menu: six tabs along the bottom, one for each of the six top-row keys, whenever a menu is open.

The lines

Plus42 decides what each line holds; the PX-42F-Plus decides how big they are drawn.

• The space below the status bar is shared equally between the lines, and each line sits in the middle of its share. So there is always space above the first line and below the last one.
• The stack's labels are drawn as X: Y: Z: T:, plus L: for LASTx and A: for ALPHA, when those are shown on top (LTOP, ATOP).
• In the large font, and in the smaller ones when there is room, a dotted line separates every two lines. It is either between all of them or none, never in some gaps only.
• A plot fills the whole area below the status bar, drawn from Plus42's own pixels at the same scale across and down.

The menu

A menu always looks the same, whatever the number of lines: six black tabs, 14 pixels tall, labelled in the small font. Each tab belongs to the key below it.

• A label is cut short at five characters.
• An item that is the current setting (for example RAD in the MODES menu while in RAD mode) is underlined.
• When a menu is open, the lines share the space above the tabs. When no menu is open, the bottom row is one more line of text and the lines share the whole area.

3. The status bar

The status bar has two halves: information on the left, and the calculator's indicators on the right.

Both bars show every indicator at once, only to show where each one appears. Normally only the ones that apply are lit.

Left: the directory, or the date and time

Plus42's HEADER setting (DISP menu, third page, HDR) chooses what the left side shows:

• HEADER on (after Memory Clear): the current directory, such as { HOME } or { HOME MATH }. After it come any extras that are switched on:
  • HFLG (HFLAGS): the numbers of any of flags 0–10 that are set, for example 13 for flags 1 and 3.
  • HPOL (HPOLAR): a ∡ while the calculator is in POLAR mode.
  • In the BASE menus, the base and word size, such as HEX 36 SW. In TVM, its BEGIN/END status.
  There is room for 22 characters. A longer path loses its beginning, shown as …, so the directory you're in always stays in view.
• HEADER off: the date and time, in the formats set in Date & Time, for example TUE-OCT-21 11:42AM or 2026-10-21 11:42.

Right: the indicators

From the right edge leftwards. These are the icons as the calculator draws them, enlarged; only the ones that apply are shown.

Icon	Meaning
	Battery: four bars when full, none when nearly empty. Always shown.
	DEG: angles in degrees. One of the three angle icons is always shown.
	RAD: angles in radians.
	GRAD: angles in grads.
	Shift: SHIFT is active; the next key does its shifted function.
	More menu rows: the open menu has more rows; ↑ and ↓ page through them.
	Running: a program is running.
	Alarms: at least one alarm is set. See Alarms.
	Printing: the calculator is sending to the printer. It's the print annunciator of Plus42 and the HP-42S. With the HP 82240B, it goes off when the last line has been sent, so the printer may still be finishing that line. See Printer.
	ALPHA keyboard: shown while you type text in ALPHA. [ ] is the HP-42S's keys, [a] types lowercase letters, [A] capitals. See Typing in ALPHA.

The angle icons are the HP-42S's own characters °, π and G. The ∡ sign is left to Plus42's HPOLAR mark on the left side, where it means POLAR mode.

4. Lines and fonts

The number of rows is Plus42's own setting, and the font follows from it: the PX-42F-Plus always uses the biggest font that fits. The row count includes the menu's row (with no menu open, that row is a line of text).

After Memory Clear the calculator starts with 5 rows and ATOP on: ALPHA, T, Z, Y and X in the large font, or ALPHA, Z, Y and X above a menu.

Changing the number of rows

Press SHIFT DISP (the E key) and page down to the third page:

Other settings on the DISP menu's later pages change what the lines show:

• HDR, HFLG, HPOL (HEADER, HFLAGS, HPOLAR): the left side of the status bar. See The status bar.
• LTOP: a line for LASTx (L:) at the top.
• ATOP: a line for ALPHA (A:) at the top.
• 1LINE / NLINE: whether a long number in X stays on one line or wraps onto more.

5. The three fonts

The calculator screen uses three fonts. Each is either the built-in one or a font of your own from the drive, chosen in Settings → Fonts.

Every font holds the 128 characters of the HP-42S character set, in the HP-42S order. Codes 32–126 are mostly ordinary ASCII, and codes 0–31 hold the calculator's own symbols:

The built-in fonts

Each map shows the 128 characters in a 16 × 8 grid. A character's code is its row (00 to 70, in hexadecimal) plus its column (0 to F).

Making your own font

A font is a PNG image, called a font sheet, with the 128 characters in a grid of 16 across and 8 down, in code order: the character with code c is in row c ÷ 16, column c mod 16. Dark pixels are ink. The sizes are fixed:

The easiest way to start is from the built-in font's own sheet. It's on the drive, in /FONTS/BUILTIN/: LARGE.png, SMALL.png and MINI.png. Copy it to the computer and edit the copy. The originals are read-only, and the calculator writes them again if they go missing or change. If your computer keeps the copy read-only too (locked, on a Mac), clear that in the file's Get Info or Properties. Copy the finished PNG into its folder with USB Drive, then choose it in Settings → Fonts.

The settings menu, the boot screen and the clock on the splash screen always use the built-in fonts. That way a font that turns out unreadable can always be undone.

6. The settings menu

Press SHIFT then EXIT to open it. Every screen has the same frame: a black title bar with the screen's name and the current time, and a line at the bottom saying what the keys do there.

Moving around

• ↑ ↓ move through a list. A > at the right of an item means it opens another list; other items show their current value there.
• ENTER chooses the highlighted item.
• EXIT or ← goes back one level. On the top list, ← returns to the calculator.
• EXIT on Off, or SHIFT then EXIT anywhere, turns the calculator off.
• Numbers are typed with the digit keys into the blanks (__:__); ← (Bsp) deletes the last digit, ENTER accepts, EXIT cancels.
• The menu turns the calculator off after the Sleep Timer, just as the calculator screen does.

The settings are saved when you change them, and are kept when the calculator is turned off, reset or reflashed.

Off

Turns the calculator off. ENTER or EXIT on this item does it.

Games & Apps

Runs programs written for the PX-42F itself: games and apps. Each is a .bin file on the drive, in /BIN/GAMES or /BIN/APPS. To add one, copy its .bin into the folder with USB Drive. To remove one, delete the file. None come with the calculator.

Only install apps you trust. A game or app is a program that runs on the calculator with full access: it can read, change and delete any file on the drive, including your saved states and programs. The calculator checks that the file isn't damaged, not that it is safe. Keep a copy of your states (USB Drive) before trying an app from somewhere you don't know.

• Leaving. ON always leaves a game or app, back to this list. Held for 2 seconds, it turns the calculator off. The Sleep Timer turns it off too.
• Your memory is safe. Before a game starts, the calculator saves its memory to the drive, and takes it back afterwards. If a game crashes or hangs, the calculator restarts with its memory as it was, and the start screen says where it stopped.
• Their own files. A game keeps its files (a best score, settings) in a folder named after it, next to it: /BIN/GAMES/SNAKE/ for SNAKE.bin.

If one can't start, the calculator says why:

Making your own. Games and apps are written in C with the PX-42F App Template, a separate project. It covers the screen and fonts, the keys, the clock, sounds, files on the drive, the USB console, the infrared LED and the battery, and it includes a simulator that runs a game on a computer. Its README explains how to start. The Snake game is built on it.

Date & Time

The formats are the calculator's own: Plus42's DMY, MDY, YMD, CLK12 and CLK24 commands change them too, and the setting follows. DOW-MON-DAY is a PX-42F-Plus format; to Plus42 it counts as MDY. The status bar (with HEADER off), the settings menu's title bar and the splash screen's clock use these formats.

Time Calibration

• Correction: choose Clock Runs Slow, Clock Runs Fast or No Correction, then type how many seconds a day it loses or gains, to a tenth of a second.
• Measured: lets the calculator measure its own drift. Type the exact time to the second (hours, minutes, seconds) and press ENTER exactly at that second. Do it again after a day or more, and at least 6 hours later: the calculator then shows how many seconds a day it gained or lost, and offers to apply that as the correction. Once something is measured, Measured offers Apply or Enter Exact Time. Setting the time exactly from a computer counts too.

The clock keeps running while the calculator is off, but a full reset (the RESET button, or a flat battery) loses the time.

Alarms

The alarms set with XYZALM, earliest first, with a date, a time and the text. A ! in front means the alarm is past due. ENTER opens an alarm to show all of it, with two choices below: Sound and Delete. See Alarm commands for how to set them.

Sound sets what this alarm plays: Plus42 tones (the default), a WAV file from /SOUNDS or a song from /MIDI. ENTER chooses a sound and plays it, and EXIT stops it and goes back. The file names are listed with their .wav or .mid ending, up to 64 of them, and only files directly in those folders. An alarm that repeats keeps its sound.

A short sound plays again once a second after the first few seconds, as the tones do. A sound longer than the alarm's 20 seconds plays to its end. Any key stops it, along with the alarm. If the file has gone from the drive when the alarm comes due, you hear the Plus42 tones instead. Clearing flag 26 silences all of them. A control alarm only runs its program, so it has no Sound. The two tones that remind you of past-due alarms at power on, or that warn of an alarm set for a time already past, don't change.

Sounds

The boot sound has no setting. It always plays when the calculator starts: after the RESET button, a firmware update or a restart, but not when you turn it on with ON. To change it, replace BOOT.wav (see Other sounds).

Key Sound

The list shows Off, the built-in key sounds, then any of your own on the drive. ENTER chooses one and plays it. There are two kinds:

• A single sound (Tick, Tock, Glass, Pop, Beep, Free42): every key makes the same sound.
• A set (built in: Typewriter): three sounds, chosen by what the key does. Choosing a set plays all three in order.

In the settings menu, ENTER makes the ENTER sound and every other key the entry sound.

Your own key sounds. Copy WAV files into /SOUNDS/KEY on the drive:

• A single sound: /SOUNDS/KEY/<name>.wav, at most 250 ms.
• A set: a folder /SOUNDS/KEY/<name>/ with ENTRY.wav, OP.wav and ENTER.wav, at most 100 ms each. A missing OP.wav sounds like ENTRY.wav, and a missing ENTER.wav like OP.wav.

Longer sounds are cut short with a fade. Short sounds (30–60 ms) suit fast typing best, because each key press cuts off the sound before it.

Other sounds

All the calculator's sounds are WAV files in /SOUNDS on the drive. Replace any of them with your own:

Any WAV that Audacity exports works: PCM (8, 16, 24 or 32-bit) or 32-bit float, mono or stereo, any sample rate. Every sound is played at full volume, whatever its level in the file. A deleted file comes back as the built-in one at the next start. A built-in sound you haven't replaced is updated by itself when a new firmware changes it. Sounds you've replaced are never touched.

Clock commands from the HP-41 Time Module

These work as on an HP-41CX, with the same XROM codes. Pick them from the Catalog's PX42 page, under CLOCK, ALARM and SW, or type them with XEQ ALPHA, from the keyboard or in a program.

• CLOCK shows the running clock on the top line. The next key clears it and does its usual job. In a program, CLOCK also stops the program, and R/S goes on. The clock stays up until the Sleep Timer turns the calculator off.
• CLKT makes CLOCK show the time, updated every second: 3:15:07 PM. CLKTD makes it show the time and date, updated every minute, which saves power: 3:15 PM 01/21. CLK12, CLK24 and the date format commands set the rest of the format.
• T+X moves the clock by X, in the form HHHH.MMSSss, forward or back with its sign, into another day if needed. Use it for time zones and daylight saving. It doesn't affect the clock's correction.
• CORRECT sets the time from X, as HH.MMSSss, and corrects the clock's rate from how far it had drifted since it was last set exactly. It only corrects the rate if that was at least 6 hours ago and the error is under 30 minutes. Otherwise it only sets the time. A longer gap gives a better result, because a key press is only good to about 0.1 s. The HP-41CX manual advises at least 30 hours. This is the same correction as Settings → Date & Time → Time Calibration.
• SETAF sets the accuracy factor from X, and RCLAF recalls it. This is the HP-41's own measure of the correction, and it isn't in seconds per day: one pulse of 1/10240 s is added every X seconds, or taken away if X is negative. 0.1 gains 84.4 s/day, and 99.9 gains 0.08 s/day. 0 clears it, as does anything from 99.95 up. The calculator keeps the correction in tenths of a second per day, so RCLAF can give a different number from the one you set, mostly for large factors: 50 comes back as 42.2.

Alarm commands from the HP-41 Time Module

These use the HP-41CX's XROM codes too. To set an alarm, put the repeat in Z, the date in Y, the time in X and the text in ALPHA, then run XYZALM:

• X, the time: HH.MMSSs, 24-hour. −1 to −11 also mean 1 to 11 p.m.
• Y, the date: in the current date format, up to the year 2199, or 0 for today.
• Z, the repeat: HHHH.MMSSs, from 1 second up to 10,000 hours, or 0 for no repeat.
• ALPHA, what it does: see the table. ↑ is on the ALPHA menu's second page, under the arrows (ARROW). In the [a] and [A] keyboards, SHIFT and the key for ^ also types it.

A label can be up to 7 characters, in plain letters, digits and symbols. Alarms wake the calculator from off, and it turns itself off again afterwards unless you press a key. They wait while you're in the settings menu or an app. A control alarm also waits while you're typing or in program mode. Clearing flag 26 silences their tones. Up to 32 alarms can be set, and a RESET or a firmware update clears them with the rest of the memory.

• RCLALM recalls the alarm numbered by X: time to X, date to Y, repeat to Z, text to ALPHA.
• CLALMX deletes the alarm numbered by X. CLALMA deletes the first whose text matches ALPHA. CLRALMS deletes them all.
• ALMNOW runs the oldest past-due alarm that has a program.
• ALMCAT lists the alarms on the calculator screen: ↑ and ↓ move, ← deletes one, and EXIT leaves. In a program it also stops the program, and R/S goes on.

An alarm set for a time already past becomes past due at once, with two tones. Past-due alarms stay on the list until you delete them or run them with ALMNOW, and two tones remind you when you turn the calculator on.

Playing sounds from a program

Four commands the PX-42F adds to Plus42. Type them with XEQ ALPHA, from the keyboard or in a program. They aren't in the catalog. For the two that play, the name of the file goes in ALPHA first:

• PLAYWAV starts /SOUNDS/name.wav from the drive. A / in the name is a folder: "TONES/TONE3".
• PLAYMID starts the song /MIDI/name.mid.
• SNDWAIT waits until the sound playing has ended. With nothing playing it does nothing.
• STOPSND stops the sound playing.

Both go on at once, and the sound keeps playing while the calculator or the program carries on, even after the program ends. The speaker plays one sound at a time, so a new sound replaces the one playing. To hear one sound after another, put SNDWAIT between them:

"BOOT"
PLAYWAV
SNDWAIT
"Canon"
PLAYMID

R/S stops the sound. If a program is running, it stops too; if not, the press does nothing else. While you're typing in ALPHA, typing a command or in program mode, R/S does its usual job, and so it does for a program waiting in GETKEY. EXIT stops the sound only during SNDWAIT, and turning the calculator off always stops it. Key presses don't interrupt the sound, and they make no key sound while it plays. Clearing flag 26 silences PLAYWAV and PLAYMID, as it does TONE and BEEP.

Nonexistent means the file isn't there, or a WAV that can't be played. Alpha Data Is Invalid means ALPHA is empty or holds something that can't be a file name. Invalid Data means a song the synthesizer can't play, and Insufficient Memory a song over 128 KB or too big for the memory left.

Fonts

Choose a font to see its list. ENTER on a font shows all 128 of its characters. Press ENTER again to use it, or EXIT to keep the one you had. A sheet of the wrong size is refused, with the size it should be. See The three fonts.

Sleep Timer

Turns the calculator off after this many minutes without a key press: 0 to 999, where 0 means never. The default is 10 minutes, the HP-42S's own. The timer doesn't run while a program runs, while Plus42's "continuous on" (flag 44) is set, or while a computer is connected over USB.

Splash Image

The picture the screen shows while the calculator is off, with the date and time across the top, updated every minute.

• Timer: how many minutes the picture stays up after turning off, 0 to 999. After that the screen goes blank. With 0, it's blank straight away. The default is 10.
• Image: Built-In, or a PNG from /SPLASH on the drive. ENTER on an image shows it full screen, as it will look. Press ENTER again to use it, or EXIT to go back. The best size is 250 × 122 pixels, and the PNG must not be interlaced. A screenshot works as is.

Showing the picture costs a little battery while off: about 200 µA against 135 µA blank.

Printer

• Off: printing commands do nothing (Plus42's PROFF).
• USB Serial: printing goes to a second USB serial port named PX-42F Printer. Open it in a terminal program on the computer to see the output. Choosing it also turns Plus42's printer on (PRON).
• HP 82240B (IR): printing goes by infrared to an HP 82240B printer, as on the HP-42S. It works only with the HP 82240B, not with other infrared printers. Aim the calculator at the printer's window. Text prints in the printer's own characters. The characters it lacks (√, Σ, π, the arrows and others) print as graphics in Plus42's shapes. Choosing it asks how PRLCD prints the screen:
  • Portrait (the first time): the screen redrawn to fit the paper, in Plus42's own small characters: the status bar's text, the lines with the dotted lines between them, and the menu. It takes about 20 seconds. The layouts of 6 rows and more are too wide for the paper; they print in landscape.
  • Landscape: the screen dot for dot, with the PX's fonts. The screen is wider than the paper, so it prints turned a quarter: turn the paper a quarter clockwise to read it. It takes about 2 minutes.
  EXIT there keeps the one chosen before. The printer can't tell the calculator when it is ready. So the calculator waits as long as the slowest printer on nearly flat batteries needs, 1.8 seconds a line. A long listing (PRP, PRV, PRUSR) takes that long, with ▶ and the printer icon in the status bar. EXIT or R/S stops it, and other keys wait until it ends. They stop PRLCD too, and a program printing with it, but it takes up to 2 seconds, because a line that has begun is always sent whole, or the printer would misread what follows. The printer also finishes what it already has, so the paper can go on for a little. Choosing it also turns Plus42's printer on (PRON).

With a printer chosen, programs print too, and VIEW and AVIEW in a program print as well as show, as on an HP-42S with its printer on. The setting sets flags 21 and 55 at every start, so a PROFF or CF 21 lasts until the calculator is next turned on.

States

A state is a complete copy of the calculator's memory (stack, variables, programs, settings) in a file. States are kept on the drive in /STATE as <name>.p42 files, the same format the desktop Plus42 uses.

Plus42 can't read Free42 states (.f42). Programs can move between the two as .raw files: see Programs.

Programs

Programs can be kept on the drive as .raw files, in /PROGRAMS. This is the program file format of Plus42 and Free42 on computers and phones, and of the program libraries online. A .raw file holds one or more programs; it doesn't hold variables or the stack (use States for those).

Both work on the programs of Plus42's current directory, as Plus42's own Import and Export do. To bring .raw files from a computer, copy them into /PROGRAMS with USB Drive. Files whose names are longer than 28 characters aren't listed: rename them shorter.

USB Drive

Info

7. Files on the drive

Everything the calculator reads from or writes to its drive, as seen in USB Drive. The calculator makes the folders by itself.

8. The back of the calculator

Looking at the calculator from behind, the openings are, from left to right:

9. Charging

The calculator runs on a built-in 1100 mAh lithium-ion battery, charged through the USB-C port from any USB charger or computer.

• The calculator can be used while it charges.
• The battery gauge at the right of the status bar shows the charge in four bars. Settings → Info shows the battery voltage: about 4.2 V when full.
• When the battery is nearly empty, about 3.45 V, the calculator turns itself off to protect it. Its memory is kept while some charge remains, so charge it soon, then turn it on again. Left empty for long, the battery can run out completely, and the memory and the clock's time are lost: save important work as a state.
• Turned off, the calculator uses very little power, about 135 µA, or 200 µA while the splash picture is showing. A full charge lasts months turned off, and many hours of use.
• While a computer is connected over USB, the Sleep Timer doesn't turn the calculator off.

10. Updating the firmware

New firmware comes as a single .uf2 file. Installing it takes a USB-C cable and a computer (Windows, macOS or Linux); no software is needed. Saved states, program files, splash images, fonts, sounds, games and apps and the settings are on the calculator's drive, which an update doesn't touch.

From the settings menu

1. Connect the calculator to the computer with the USB-C cable.
2. Open Settings → USB Drive → Update Firmware and press ENTER. The new firmware starts with the memory cleared, as after any update: save the memory first if you want it back (Settings → States → Save State). Then a new drive named RP2350 appears on the computer: that's the update mode. The screen shows what to do, and the keys do nothing meanwhile.
3. Drag the .uf2 file onto the RP2350 drive.
4. Wait. When the copy finishes, the drive disappears by itself and the calculator starts the new firmware, with the memory cleared and the time as it was. The computer may warn that the drive was removed without ejecting it; that's normal here.

With the BOOT and RESET buttons

If the calculator doesn't respond, or to install firmware older than the Update Firmware item. This way clears the memory and may lose the time: save the memory first if you can (Settings → States → Save State).

1. Connect the calculator to the computer with the USB-C cable.
2. Press and hold the BOOT button.
3. While holding BOOT, press and release the RESET button.
4. Release BOOT. The RP2350 drive appears.
5. Drag the .uf2 file onto it, and wait for the calculator to start.
6. If you saved your memory, load it back: Settings → States → Load State. Set the time in Date & Time.

To check the update, Settings → Info shows the firmware version and the date it was built. To leave update mode without installing anything, press RESET. Like any RESET, it clears the calculator's memory.

11. Added commands

The PX-42F adds these 31 commands to Plus42. They are all on the Catalog’s PX42 page: press SHIFT + (CATALOG), then ↑ once. Its tabs are CLOCK, ALARM, SW, SOUND and DRAW. Names too long for a soft key show shortened, as Plus42’s own do: CORRECT is CORCT. The table gives each short form. Program lines always show the full name. Pick a command to run it, or to enter it in a program in program mode, or to assign it to a CUSTOM key after ASSIGN. You can also type them with XEQ ALPHA. Plus42’s own DATE, TIME and the like stay under the Catalog’s TIME tab.

The clock, alarm and stopwatch commands work like those of the Time Module for the HP-41C, which is built into the HP-41CX. They have the same names and the same XROM codes. The sound and graphics commands are the PX-42F’s own, because the Time Module has none, and they use XROM 0, which no HP-41 module uses.

Each heading in the table links to the full description of its commands. Plus42 already has the Time Module’s date and time functions, such as DATE, TIME, ADATE, ATIME, DOW and DDAYS, so they aren’t listed here.

Some of the Time Module isn’t here. ALMCAT has no T, D or R keys. Past-due alarms don’t activate when you turn the calculator off.

Only the PX-42F runs these commands. A program that uses them can be exported to a .raw file, but Plus42 on a computer or phone shows them as XROM 26,nn or XROM 00,nn, and running one gives Nonexistent.

Stopwatch

The stopwatch works like the one in the HP-41CX. It runs until you stop it, whatever else the calculator is doing, also while it is off. Setting the clock doesn’t change it. Memory Clear resets it, and so does a crash that restarts the calculator, to the time it had at the last OFF.

SW shows the time on the top line and gives the keyboard to the stopwatch until you press EXIT. Leaving doesn’t stop it. In a program, SW waits there, and the program goes on after EXIT.

00:00:12.3 >R00

The end of the line is the register that the next split goes to. > means splits are being stored, = means one is being recalled, R shows plain splits and D the differences between them. While it runs, the time shows to a tenth of a second. When it stands still, it shows to a hundredth.

Splits are stored in the data registers as HH.MMSSss, replacing what is there. It beeps when the pointer reaches the last register. A split with no register to go to, or a recall of one, ends the stopwatch’s keyboard with Nonexistent. ERROR =R05 means that register doesn’t hold a time, and ERROR =D05 that it isn’t later than the register before it. Move the pointer to clear it.

SWPT takes the storing pointer and the recalling pointer from X as sss.rrr, so 12.003 stores from register 12 and recalls from register 3. A negative number starts with differences showing. After EXIT, X holds the pointers in the same form, and LAST X holds the number you gave it.

As a timer: set a negative time with SETSW and start it. When it reaches zero it keeps counting up. If the stopwatch’s keyboard is on, you hear two tones. Otherwise TIMER ALARM sounds and flashes like a message alarm, and turns the calculator on if it is off. Any key ends it, and it doesn’t become past due.

Alarms wait until you leave the stopwatch’s keyboard. The Sleep Timer doesn’t turn the calculator off while the keyboard is on, and the screen updating 10 times a second uses about as much power as a running program. RUNSW, STOPSW, SETSW and RCLSW don’t show anything, so a program can time something without changing the screen.

Graphics

The graphics commands draw on the whole screen, 250 dots across and 122 down, whatever the number of rows. 1,1 is the top left corner, as with PIXEL and AGRAPH, and 250,122 the bottom right. The status bar's rows are 1 to 12. The numbers stay on the stack.

PEN sets what the next shapes use, and stays until you change it or turn the calculator off:

• X, the color: 1 black or 0 white. White erases what's under it, including text.
• Y, the width: 0 filled, 1 one dot, up to 64. A line can't be filled, so 0 draws it one dot wide. A box's or an ellipse's outline grows inward, keeping its outer size. A line's width is centered on it, with round ends.

The pen starts black, one dot wide. A filled black circle in the middle of the screen, with a white box inside:

CLLCD
0
1
PEN
126
62
40
40
ELLIPSE
0
0
PEN
106
52
40
20
BOX

Plus42's PIXEL and AGRAPH draw on the same 250 by 122, so all of these line up, whatever the number of rows. PIXEL is always black, one dot, and AGRAPH keeps its modes (flags 34 and 35). WIDTH and HEIGHT give 250 and 122. A program written for the HP-42S's 131 by 16 draws at its true size, in the top left corner.

Drawings stay until the next key, or until CLLCD, and also after a program ends, as on the HP-42S. To end a program with the stack back on the screen, make CLD its last step before STOP. The status bar and the dotted lines between rows are hidden while they show. To keep the stack from showing under them, start with CLLCD. Printing with PRLCD to the HP 82240B prints them, always in Landscape; printing to USB doesn't include them. POLYGON takes up to 64 corners; where its edges cross, a filled one has holes.