Subroutine tactics for the HP-25


Hello all,

Although my 25C may have amnesia, I'd rather salvage my 25C for its functionality.

Since I also have a 55, I've been pondering the idea of implementing subroutines although there is only GTO on both.

Although one idea like the 'Newton's Method' program in the HP-25 Applications Book which build the Newton algorithm surrounding the user function, one idea I was toying with is something like this:

01 1
02 [RCL] 1
03 [GTO] 33
04 0
04 RCL 2
05 [ABS]
06 [GTO] 33
07 [FRAC]


33 [log]
35 [x=0]
36 [GTO] 04
37 [GTO] 07

In other words, although a simple example, what's in the Y register controls where the [GTO] instruction transfers to at step 35 for both the first and second time the subroutine is called.

Any ideas of other approaches to subroutine techniques on an HP-25 and 55 are welcome as I am looking for new techniques to increase the functionality of my 55 and 25.

Edited: 16 Apr 2012, 9:57 p.m.


Since I also have a 55, I've been pondering the idea of implementing subroutines although there is only GTO on both.

Have a look at this 7-page PDF article:

Long Live the HP-25 !

featuring an HP-25 program which manages to call a two-variable user-defined function no less than 4 times with different arguments each time while always returning to the proper place in the computation procedure, and not only does it fit in 49 steps but actually leaves as many as 13 steps free to define the f(x,y) function.

You may get some good ideas for subroutine-like implementation by carefully studying it.

Regards from V.


Thanks very much! To be honest, my train of thought has been greatly refined here at MoHPC Forums. This group has helped me think beyond my usual instincts. I am very grateful for your help and all those here.


You need to obtain a copy of "Computational Analysis with the HP-25 Pocket Calculator" by the late Peter Henrici published by John Wiley & Sons.

Trent Moseley

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