HP-25 Happy Anniversary !! My take

[Valentin Albillo]

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Hi, all:

I became aware of this momentous event when reading Willy R. Kunz's thread (check it, he also announces a brand new powerful HP-25-related creation of his):

Happy anniversary, HP-25!

and I don't want to let the event pass by without having my take on the subject, as the HP-25 was my very first HP calculator 45 years back and owning it and using it probably changed my life for the best.

This is what I wrote about it in my HP site, with links to three PDF documents:

• This is my very first HP calculator, the wonderful HP-25, the smallest and cheapest HP programmable calculator at the time. Released in 1975 (some 44 years ago as of 2019) it still looks and works perfectly.
  
  It has 10-digit with 2-digit exponent, classic RPN stack, 8 storage registers with full storage arithmetic, a vast range of math functions including statistics, solid build and very small size, bright LED display fully useable in very low light or even utter darkness, excellent reliable keyboard, extremely good and comprehensive documentation (including tons of good application programs for all disciplnes), good programmability (49 fully-merged steps) with tests, branching, and single-step execution for debugging, etc. Also, an updated version, the HP-25C, dotted it with Continuous Memory, another first at the time.
  
  You'd need to have lived through those times in order to fully understand what the HP-25 meant for both professionals and students like me back then, but failing that, you can find some of my programs for it in the HP Calculator Programs section in this very site, which will give you a fair idea. Meanwhile, you should really have a look at this Article of mine for a detailed review, including two truly amazing sample programs for you to see for yourself what it could do when pushed to the absolute max:
  
  Long Live the HP-25, (7-page article, includes two programs to solve 1st-order ordinary differential equations using Runge-Kutta methods of 3rd and 4th order, resp.)
  
  Also, have a look at the following programs I wrote which extensively discuss and feature the HP-25:
  
  HP-25 Solving 2nd-order differential equations, (numerically solves 2nd-order differential equations of the form y”=f(x,y) subject to initial conditions, using a 5th-order method)
  
  HP-25 Gamma Function and Factorials, (accurately evaluates the Gamma function in the interval [1, 2], and also approximates factorials for real-valued x)

Regards.
V.

[Gene]

Great article - Long live the HP-25... and what a fabulous image of the HP-25!
Gene

[bshoring]

Great post. And I’ve long loved your article “Long Live the HP-25.”

[BillBee]

Well done and said. I must say enjoy reading the "Long Live" documents on your site.

Thanks!
Bill