Calculator blog

Musings and comments about our common interest


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A Time module to go with a HP41CL

We have just found a Time Module - which will be available for the HP41CLs that we have for sale!!


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Time module in HP41CL


So far the hp41cl doesn't provide a clock to be used as time module, and it requires a working one to be able to function as stopwatch or alarm clock (or launching programs at a defined time)

However, the hp41cl "raw" provides all the time-related calculating functions of the time module: days difference between two dates, date calculations, etc. So, if you don't want the above clock features, you can live without it (and why would you want them when you have a smartphone?)

There are always those that would like to have the full Monty (never better said when referring to Monte’s development), and then you may want to have the time module too. Or, you have interfaced your hp41c with other items, and then you need to launch programs at a determined time intervals. 

I once did that, when I connected a HP3468A HP-IL multimeter to the HP41CL to check what was the voltage in my weekend cabin during an extended period of a week. Then it was grabbing data every half hour for the whole Monday to Friday we’re not there. 

Other uses that we’ve seen are: 

- use it in conjunction with astronomical programs, to better direct your telescope.
- Use it during flight to calculate fuel consumption rates, direction drift on side winds during time periods, etc. 

As always, here is no reason this couldn't be done with a smartphone - but if you don't have the program that does what you want, then the easily programmable HP 41CL can come to the rescue nicely.

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Time module on sale

DSC_7332We have sourced an original Time Module for the HP41C  available at 150 € plus shipping. If bought together with a HP41CL  he price is reduced by 30 € - please contact to organize (there are two HP41CL left).

This time module comes with a user manual in French

There is as well a HP41CL based on version 3 of the circuit - it is sold at 470 €, with a discount of 140 € over the v4 (and latest) version.

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A new time module on sale in a few days

IMG_1639I have found another Time Module. This time, it comes with manual in good shape and quick reference card, both in English.

It will be put on sale at the price of 150€. If you’re really interested and want to get it, please send me a mail to

Those of you that have a HP41cx don’t need it - this model came with it. Bot for the other owners of a HP41C, it is probably the most significant module - together with the advantage pac. And if you have paid a lot of money for a HP41CL, you deserve to have the full Monty.

The legend tells that the time module was developed under NASA requirements, so that the Columbia shuttle astronauts could have a calculator that could substitute the Shuttle computer, “just in case”. One of the programs that was installed (and that would require the likes of a time module) was used to search for the right ground station to send data or receive communication from. I have heard also of programs to calculate the best orbit exit routes - also requiring accurate timing. But sources did not agree on whether these programs had been loaded “just in case” or the calculator was really used for number crunching and actually relieving the main calculator from some tasks.

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