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Full Version: HP 15C Displaying Incorrect Values!
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Hi,

My HP 15C displays the correct numbers for ln(2/3) but says it is positive!

Complex mode?

Even in Complex mode the answer is negative.

Jeff Kearns

Try something simple:

type 7 CHS

do you see

- 7

or do you see

7

?

If the latter, you have a dead segment in the display.

Quote:
Try something simple:

type 7 CHS

do you see

- 7

or do you see

7

?

If the latter, you have a dead segment in the display.

Luckily I see the first! I have absolutely no idea what I did, but it is now working! Could someone please tell me what the complex mode is, and how it affects answers, because I am writing an exam on Thursday, and it would be disastrous if all my calculations were wrong because of my calculator? :D

Oh, and does anyone know where you can get cases for the HP 15C, and the original manuals? Not a PDF format, but a hard copy?

Thanks again.

Quote:
Could someone please tell me what the complex mode is, and how it affects answers, because I am writing an exam on Thursday, and it would be disastrous if all my calculations were wrong because of my calculator?

In complex mode, you work with complex numbers instead of plain ol' real numbers. If you're not familiar with complex numbers, you can read about them on Wikipedia or Mathworld, so I'm not going to explain them here. Just to make sure that they don't trip you up,
you can turn complex mode off by clearing flag 8: [g] [CF] 8

Quote:
does anyone know where you can get cases for the HP 15C, and the original manuals? Not a PDF format, but a hard copy?

eBay. Oops, I guess I was supposed to say "TAS".

Please don't take offense, but are you absolutely, positively sure that you did not take ln(3/2)?

Regarding complex mode, like Eric said it is a mode that accepts complex numbers as arguments to functions, and returns complex numbers when appropriate. It is activated on the 15C by setting flag 8 (g SF 8), or by pressing f I. When active, it creates a parallel, unseen stack which holds the imaginary components of complex numbers. The real portions are held in the regular viewable stack. A small "c" appears in the lower right of the screen when in complex mode. The biggest potential gotcha is that all arguments are treated as radians for trigonometric functions when in complex mode, regardless of the angular mode setting of the calculator. So in complex mode, sin(60) will return -0.3048 instead of 0.8660.

..

Edited: 20 Apr 2011, 7:42 a.m.

Be sure you know your calculator before using it in your exam. Verify you know RPN. Then your 15C will serve you well for sure.

Quote:
Please don't take offense, but are you absolutely, positively sure that you did not take ln(3/2)?

Well, I am positive I did, but nevertheless, the keystrokes I made are as follows:
2 {Enter}
3 {/}
{g} and then {e^x}

Quote:
Be sure you know your calculator before using it in your exam. Verify you know RPN. Then your 15C will serve you well for sure.

I love RPN, and have been using it for three years. How do I know if both my HP 35s and HP 15C are in complex mode?

Hi Ian,

I think the reason Walter said that is that if you do:

```3
enter
2
/
Ln
```
you get 0.4055,
whereas if you do:
```2
enter
3
/
Ln
```
you get -0.4055, and this inversion can happen if you accidentally do your operations infix instead of postifx.

For edification,

```Ln(2/3) is carrried out as
2
enter
3
/
Ln
```

The 35s does not have a complex mode in the same way that the 15c does. To learn how it works, refer to your manual. It can also be downloaded. In addition, you can buy the 15c manual in PDF by buying the appropriate museum dvd(s) or cd(s).

The 35s does not give complex answers unless it was given a complex argument, e.g. -2 {LN} returns error "LOG(NEG)" but -2+0i {LN} returns 0.69314718056+3.14159265359i. So it should not be a concern when working with real numbers.

Note that complex number display depends on settings and can be either xiy, x+yi or r@a (where @ represents theta symbol).

Cases: You can shop around for any case that will fit the HP-12C (which is still sold).