41 cx time


My 41cx has lost time over a 24 hour span about 9 mins, this seems very excessive.
Is there any way to calibrate the timer?
I have a halfnut.

Thank You
GS Leong


Hi, Leong;

there are two ways to "calibrate" the CX clock.

first one - enter the actaul time in the X-register and execute CORRECT at the exact moment this time is reached. CORRECT computes the difference between the internal clock and the value in the X-register, and uses the difference to balance the internal "ticks"

second one - use SETAF (set accurace factor). This function uses the value in X-register to force a "stable drift" and adjust any unaccuraces.

If you have the HP41CX Owner's Manual, Vol. 2, please check pages 238 and 376. If you don't have it, post again and we'll add more info.

Best regards.

Luiz (Brazil)


Thank you Mr. Vieira for your time.

That is all the info I need on the subject.

GS Leong


Hi GS Leong,

I am sorry but 9 mins per 24 hours can't be corrected by the functions CORRECT or SETAF.
SETAF can correct 84.375 seconds per day with the value SETAF = 0.1

The function CORRECT has the same range as SETAF.



Were all the cx's bad about accuracy or is this one just way off?

GS Leong


I bought one in 1984 (fullnut, Singapore made) and it was fine.

Not as accurate as my wristwatch, but by twiddling the accuracy factor, I could get it to within a few seconds per day.

Yours probably has a bad crystal?


>Were all the cx's bad about accuracy or is this one just way off?

My 41cx halfnut's clock is off by a couple of minutes per year with no correction factor. I only set it when we go on or off daylight savings time. Actually, I usually do 1 or -1 T+X.


Hi GS Leong,

my 41 CX looses 1.07 s per day without correction.
With correction it is better than 0.03 s per day.

I make notes about the drift and I use the formula
on page 377 (HP 41 CX German handbook) to calculate
an improved AF (accuracy factor).

Kind regards,

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