RPN-55 SD — The first photo-realistic HP-55 simulator for the iPhone

Version 1.0

RPN-55 SD is a photo-realistic simulation of Hewlett-Packard's classic scientific calculator HP-55.

Released in early 1975, the HP-55 was the lower-cost alternative ($395) to the famous HP-65 ($795). Its main feature was a quartz timer. The HP-55 was discontinued in 1977.

RPN-55 SD is a fully compatible version of the HP-55 with twice the program memory.
By setting a simple switch, you can turn on a number of useful extensions.

"The HP-55 features more pre-programmed functions than any other scientific pocket calculator in the world." (Owner's Handbook, 1975)



Tap the wrench symbol or double-tap the display to access the
settings screen:

iPhone X Screenshot:
(extended mode)

Register View:




HP-55 Brochure (in German)
Published in March 1975 by Hewlett-Packard, Switzerland. Download

Price List – Note that 1,195 Swiss francs in 1975 ≈ $2,300 in 2019.

HP-55 in HP-65 User's News
Hewlett-Packard introducing the HP-55 in the first issue of "HP-65 User's News", mid-1975: Download



Version History RPN-55 SD

1.0 – July 2, 2019
  • First public version.


RPN-55 SD is available here:



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