Recognizing HP 41 model (C, CV or CX)


I have the opportunity to buy a 41 but the buyer as a doubt about the version. The front plate clearly shows 41CX but he’s not able to find any time functionalities.

So, what could be a ‘simple test’ to check the version?

Please keep in mind that I have to explain this to him without having a 41 myself !!!

The serial number of the calculator is 2350S40219.




one of the simplest tests to recognize the existence of the timer module is by pressing [SHIFT][ON] after having the calculator turnned on ([SHIFT] is the golden key, that activates the SHIFT indicator in the display). If it simply turns itself off after the [SHIFT][ON], then it is surely not an HP41CX or it has a bad time module. Also, try [SHIFT][CAT][2]. You should see:

[TIME FCN 2_ ] (the underscore represents the version indicator)
[EXT FCN 2_ ]
Any other HP41 (C or CV) will do nothing after CAT 2, unless it has a ROM module plugged in or, if hacked, an internally connected extra ROM.

Hope this helps.

Luiz (Brazil)

Edited: 23 Sept 2005, 5:05 p.m.


There must be many ways to tell a cx from a cv with modules in it, but one extra-quick one should be to try the catalogs above catalog 3. The cx adds catalog 4 for files in extended memory, catalog 5 for alarms, and catalog 6 for key assignments. I think that if you try these on a c or cv, you'll just get catalog 3 (like you do if you try "catalog 7" on a cx).


Catalog 2 (yellow shift - Enter - 2) will show the list of available functions. My CX displays:

Best regards


Hi, Peter;

you are right. I don´t have my CX in hands right now, and the [TIME 2_ ] plus [CX TIME ] are the correct output messages.


Luiz (Brazil)


Hi Francis,

One way to find out if the 41 is a CX version is to do a catalog 2.

Shit Key (Gold Key)

Enter Key


This will run the system catalog for plugged in modules/devices. The CX funtions will show up as

-CX Time



Sorry about the misspellings. I hit the post button by mistake while trying to click on something else.


Hi Francis.

You can try to view the CLOCK:



Or try to display the current time:

[XEQ][ALPHA]t i m e [ALPHA]



You could have him clear the unit back to factory defaults with a simple proceedure.

  1. Turn the unit off
  2. Press and hold the backspace[clx a]
  3. Press and release ON
  4. Release the backspace
  5. MEMORY LOST appears
  6. Turn off and back on again to clear message
  7. Press PRGM
A CX will display 219 free registers, a C or CV will display 46 free. Not a conclusive test but sometimes worthwhile.

Many thanks to all of you guys...
That's exactly what I looked for...


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