HP15C problem


can anyone help with a problem on my old 15C. Üser"is displayed plus "C" and the calculator does not produce correct answers. Also only registers 0-2 are available. The rest come up with error 3. I presume the unit has fallen into complex maths but as the manual was a casulaty of a rainstorm in deepest Africa I have no recourse to sort it out.


Hi, Mel;

please, locate the [USER] inscription over the [RCL] key. Because [USER] is printed in yellow (gold?), you should press and release [f] then press and release [RCL] to toggle USER mode on and off. To simplify, we use

O.K.? Now locate the [CF] inscriptiopn in blue, in the front, slanted face of the [5] key. Because it is printed in blue, we must press and release [g] then press and release [5] to compose the partial sequence [g][CF] (which stands for Clear Flag). Now press the [8] key and the cannunciator should be turnned off. This sequence is also refered to as
. This means your calculator is no longer in complex mode, opnly real data and real results are allowed.

Now press

and hold the last pressed key for a while ([MEM] is located in the slanted face of the [RCL] key). You should see four numbers, something like this:
[  2  10  0-0 ]
This special display tells you how is the HP15C memory organized at this moment. The first number, 2 in this case, is the number of the last available memory register. The maximum possible set for memory registers is the sum of the first and second numbers in the left. In this example, we can set the calculator to work up to register #12. In your case, check what is the second number and compute what you have interms of memory. To change this, please locate the [DIM] function over the [SIN] key and the [(i)] function, over the [COS] key (they are neighbors). As they are printed in yellow... let's consider that you have seen the display shown above when you pressed [g][MEM], so you can set the register size to a maximum of 13, from R0 to R.2 (register #12). Than you can press:
12 [f][DIM][(i)]
Now if you press [g][MEM] you'll see:
[ 12  0  0-0 ] (based on previous display)
Now you can use registers from R0 to R.2.

If you do not succed in this (or any other) operation, please post again.


Luiz (Brazil)


Mel --

Well, I certainly couldn't surpass the detail in Luiz' response! I could offer a few insights, however:

  • Doing a "master clear" (with calculator off, hold down [-] key, then press and release [ON] key) will clear the complex-mode "C" annunciator and set register R19 as the highest-numbered allocated register. R19 is the highest directly-accessible register.

  • Setting R7 as the highest allocated register -- 7 [f][DIM][(i)] -- will allocate eight numbered registers and leave 59 unallocated registers for convenience, and will allow statistical summations to be performed (see table on backplate).

  • R0 and R1 cannot be de-allocated, because they are needed as matrix row- and column-pointers. The indirect register I also cannot be de-allocated. Thus, there are always at least three directly-accessible storage registers at your disposal.

  • Up to 64 registers can be left unallocated -- just enough to store an 8x8 matrix, or to solve a linear system of four complex-valued variables using a special procedure.

  • When you do a "show memory" operation -- [g][MEM] -- mentioned by Luiz, the first three numbers displayed will add to 65, less the number of registers used for the following purposes:

    Matrix storage (1 register per element)

    Complex mode (5 registers for the parallel stack with LASTx)

    Numerical integration in progress (23 registers)

    Numerical rootfinding in progress (5 registers)

  • All stored matrix elements can be cleared at once using [f][MATRIX] 0.

  • All programming can be cleared at once using [f][CLEAR PRGM] in Program mode.
-- KS

Edited: 28 Apr 2006, 1:30 a.m.

Possibly Related Threads...
Thread Author Replies Views Last Post
  1984 HP15C rattles Footloose (Illinois) 4 918 10-15-2013, 09:43 PM
Last Post: BobVA
  HP15c continued fraction for Ln(Gamma) Tom Grydeland 0 510 09-30-2013, 05:48 AM
Last Post: Tom Grydeland
  HP15c LE emulator with unlimited number of activations Nick_S 23 2,970 01-24-2013, 03:59 PM
Last Post: Victor Quiros
  battery test for the HP15c Limited Edition Guido (Canada) 3 804 01-03-2013, 08:17 AM
Last Post: Jeff O.
  uRCL* on HP15C Csaba Tizedes (Hungary) 2 654 12-29-2012, 06:09 PM
Last Post: Luiz C. Vieira (Brazil)
  HP15C strange complex number behavior Mike W 5 984 09-11-2012, 04:36 PM
Last Post: Mike W
  HP15C Paul Averis ( Australia ) 1 554 06-18-2012, 03:33 AM
Last Post: Alexander Oestert
  HP15c LE - highest serial number over 23.000 Jose Gonzalez Divasson 1 580 05-16-2012, 03:19 AM
Last Post: Torsten
  HP15C LE Price Lowered by HP Namir 23 2,521 02-05-2012, 05:34 PM
Last Post: Andreas Grund
  HP15C LE Pause Operation not as expected Russell Dobson 13 1,622 02-03-2012, 05:43 PM
Last Post: Marcus von Cube, Germany

Forum Jump: