HP-41 - The Ultimate Calculator

There is such a thing as an Ultimate Calculator. It was made by Hewlett Packard and was named HP-41. I call it the UC-41. Along with the appropriate programs, it can do almost anything you want it to. This is of course subjective. Given enough brain washing, this will be true for you too :)

My collection

HP-41CL: The modern HP-41 calculator

HP-41CL is a brain transplanted HP-41- a new motherboard in the original HP-41 body. With huge amount of flash memory, it contains all known HP-41 roms. And with 50x turbo speed, you have a massive, superfast swiss army-knife calculator. The HP-41CL board is created by Monte Dalrymple and sold through his company, Systemyde.

I have created some solutions for the HP-41CL:

My modules

I have created a few modules for the HP-41:


The most useful of my FOCAL programs below is now contained in one 4K ROM image- the ISENE.ROM. Here you will find the Ultimate Alarm Clock, the PDA programs NOTES and REM as well as CRYPT to encrypt and decrypt ascii files and other neat stuff for your HP-41.


This ROM (module) for the HP-41 calculator is a collection of the most essential programs, utilities and tools. It is what I need, and as my needs change, so will the content of this ROM. Some programs are FOCAL, others are MCODE. Some written by me and many copied from brilliant programmers since the inception of the HP-41 some 40 years ago.


The amateur astronomy rom for the HP-41 calculator: Telescope and observational utilities. The module’s main program is “GAZE”: This is a full fledged observation logger for amateur astronomers. You add your observation equipment (telescopes, occulars/eyepieces, barlows and filters). You create your observation agenda/list for the night and then enter your notes for each object as you observe. You can create templates as observation list and use mass storage to save/load them via HP-IL.


This ROM serves two programs; “DATA” for statistical data entry and management of both single and double variables, and “STAT” that does curve fitting and statistical analysis of single and double variable data sets. The “STAT” program has taken its main part from William Kolb’s book “Curve Fitting for Programmable Calculators” with the added basic statistcs, momentums, kurtosis and skewness of data. You will find Kolb’s excellent book over at hp-41.org.


A complete gladiator arena fighting game for the HP-41 calculator. Fight your way up the ranks to become a legendary gladiator in a medieval arena. You create your character with his special attributes, weapon and armor. You enter the arena to fight a contender that roughly matches your abilities. You gain experience by winning fights, and experience can give you better attributes or buy you better weapons or armor. Each arena level consists of four fights. By cunning tactics and the luck on your side, you may advance beyond the fifth level and become a legend.


This is the main companion module for the physical NoV modules - an excellent memory expansion for the HP-41 by Diego Diaz. It contains special routines to get the most out of these Non-Volatile RAM modules as well as advanced HEPAX functions, advanced Extended Memory functions and some really neat utilities.

FOCAL programs

My most useful FOCAL programs (many are contained in the ISENE ROM):

  • DATA and STAT - The mother of all statistical analysis. Work with single or double points data sets, save and retrieve from extended memory, analyse and curve fit.
  • EVAL - A tool for making the best choices in life. The evaluation of cases against requirement specifications becomes a breeze.
  • ASTRO - user interface for the ASTRO2010 module (you will find it at hp41.org).
  • UAC - the HP-41 Ultimate Alarm Clock.
  • REM - the HP-41 REMembering (event manager, PDA).
  • NOTES - the HP-41 quick notes taker.
  • CRYPT - Encrypt/Decrypt XM ASCII files.
  • SCOPE - Calculate values for telescope and occulars
  • OUTSOURCING - Gain/loss, break-even and risk analysis if IT outsourcing
  • BOAT - Calculate properties of a sail boat.
  • D-W-D - A date-to-weeknumber-to-date converter.
  • SLA - Calculate guaranteed uptimes and allowed downtimes.
  • SUBN - Subnet mask to # of IP addresses.
  • W Lambert - Calculates the W Lambert function.
  • FILEMAN & FILE - File management system.
  • LIBXM & LIBHPX - Utilities to manage XM and HEPX files.
  • CLR - My HP-41 clear routine with basic astronomy info.

Other Tools

A set of useful tools for programming the HP-41:

  • HP-41 Coding Standard - a standard for HP-41 programs.
  • pc41 - facilitating serial/USB connection to an HP-41. With this program you can use your PC as a printer for an HP-41 (with Diego Diaz’ USB41 module) or transfer modules/data to/from an HP-41CL (with the serial interface)
  • lifasread - a Ruby script to read an ascii file stored in a lif-formated file (used by the HP-41 as file format on mass storage mediums. Tested on Linux. Run the script with the -h (or –help) option to see how it is used.
  • lifaswrite - a Ruby script to write a text file to a lif-formated file (the reverse of “lifasread”. Run the script with the -h (or –help) option to see how it is used.
  • HP-41 VIM syntax - gives you syntax highlighting in VIM when writing HP-41 programs (code on Github).
  • HP-41 VIM ftplugin - gives you tools to more easily write HP-41 programs in VIM (code on Github).


This page is an attempt at elevating the HP-41 to the ultimate calculator (the UC-41) by giving you good quality, useful software. Here is a list of further resources:

To let you in on a secret: HP rot13 is UC, and 41 rot13 is of course 41 in base 13 :) Hence, UC-41 = HP-41 rot13.

My collection was featured on Norwegian national television just a couple of months before it all burned to the ground in one of the biggest fires in Oslo in recent times. I restarted my collection after that event and I now have more than 100 calculators - most of them on display in my living room.

Here’s an article I wrote for HP: From little nerd to calculator enthusiast

And a video from when me and Arne Helme gave a talk to HP about their calculators: