Help with HP15C


Please, can someone tell me what is the procedure to perform a self check on a HP 15C?
do not have a manual.
Thank you.


press&hold "."
press "on"
release "on"
release "."



the procedure is:

while the calculator is off, press and hold the [×] (times) key;

turn the calculator on while holding [×] down;

release the [×] key.

This procedure is also known as [ON]/[×] self test.

You'll see [ running ] in the display, flashing for about 23 to 25 seconds. After that, the self-test resumes and all possible segments in the display lit, meaning it's OK. If there's something wrong, [ Error 9 ] is the warnign message.

BTW, [ON]/[.] toggles between dot and comma for radix mark.


Luiz (Brazil)

Edited: 12 May 2005, 4:02 p.m.


There is a c in the display above the CHS key. What does this mean and how can I get rid of it. Is this a complex number operation? I lost the manual and don't want to buy one for $15.

This is indeed a workhorse. I've had mine for 20 years through college and beyond.



Hi, Pamela;

the small 'c' in the display means your HP15C is ready to calculate with complex numbers, in the form 'a + bi', where 'i' is the square root of (-1). If the 'c' is in the display and you try to compute the square root of (-2), you get no error message and a 0.0000 in the display, meaning the real part of the square root of (-2) is zero, and in this case there is a complex, not-zero component, equal to the square root of 2.

To get rid of the complex mode, locate the [5] key and check for a [CF] printed in blue, in the slanted face of the key. Now, press:

[g][5][8] (AKA: [g][CF][8])
This should de-activate the 'c' indicator and put the HP15C back in real-number mode.

If you want to work with complex numbers again, you can activate the complex mode by using one of the following three sequences:

[f][Re<>Im] (printed in yellow over the [-] key);
[f][I] (printed in yellow, over [TAN] key};
[g][SF][8] (printed in blue in the slanted face of the [4] key)
There are some conditions that do not allow complex mode to be activaded: not enough registers available in the common segment (at least five) or having a matrix description in the x-register ([Re<>Im]).

There is a lot more about the HP15C, so if you need help just let us know. One of the guys that constantly declares his acquaintance to the HP15C is Valentin Albillo, an active contributor that has written many good material about it. They are all good choices of reading.

Best regards and success.

Luiz (Brazil)

Edited: 25 May 2005, 11:44 p.m.


Thanks. This has been driving me crazy. I even took the batteries out but the trusty memory kept it. This was inadvertantly turned on somehow by my 3 year old. I haven't used the complex numbers in a while but at least I had an idea what it meant.

Thanks again,


p.s. If you have financial or fountain pen questions, I'd oblige.


Thanks, Luis, for your detailed answer!

I lost the (HP-15C) manual and don't want to buy one for $15.

Actually, the going rate is now US$25-$35 (but well worth it, in my estimation).

For less money, you could buy CD-ROM #1 from this website, which includes scans of both the HP-15 Owner's Handbook and the HP-15C Advanced Functions Handbook.

This is indeed a workhorse. I've had mine for 20 years through college and beyond.

What? You didn't learn everything about it back then? :-)

Seriously, I also bought my 15C in college almost 22 years ago, and hardly ever need to consult the manual after having learned how to use the advanced functions. Almost everything about the 15C is intuitive, but getting out of Complex mode (g CF 8) is one of the few things that isn't.

-- KS

Edited: 25 May 2005, 11:40 p.m.


...or try here: Do you Know where I can found "HP15C Advanced Functions Handbook" in pdf form? (Except the Museum's CD-ROMs... :) )




You can find the HP-15C Advanced Handbook here.

Best Regards,



Dear Eamonn!

Thank you very much this link! This is really wonderful! I think I will turn back to my 15C - again! Thanks!



Hi, Csaba:

Csaba postes:

"I think I will turn back to my 15C - again! Thanks!"

Good, you're on the rigth path again ! :-)

Let's see those wonderful HP-15C applications of yours !

Best regards from V.


:) thank you, Valentin!

In this Saturday I will take my English exam, then I'll grab my 15C, and I'll code something... I don't know, what I'll do... Maybe I'll choose one of your Challenges :) Or maybe one of my hydrodynamical problems... Or something else... "And where shall I go now? The net is vast and limitless."


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