GO-21 SciRPN

This calculator was the best around in 1975 and saw me through college in electronic engineering. It is a RPN (reverse polar notation) unit that's is a powerful method of doing calculations without the need for brackets and "equal" buttons. Once one get used to entering the numbers on a stack and then choosing an operation, it makes for fast and logical processing. In 1992 I up graded to a HP 48S which can do much more mathematics than I am able to understand. A truly wonderful machine, but with this comes complexity and is not as easy to use as the 21 which does almost everything I need. I love the HP 21 and glad I can enjoy it on my IPad.

I've been after a 21 for decades. This is probably the closest I'll ever get to owning an original. Love this calculator for many sentimental reasons.......would be great if there was a way to include the full user manual as well. Great job!!!

I still have a working HP21 and use it almost daily - this app puts it on all my iHandhelddevices. It is just like the real thing - except with visible memory and stack (that you can hide under the calculator if you want to). I have bought several RPN calculators for iPhone - this is the first to not dissapoint. Side note... The Hewlett Packard 20 series calculators (Woodstock) were released in the mid 70's, at the time they were state of the art technically and in terms of industrial design. HP developed far more powerful calculators, but the HP21 & 25 remain as a benchmark for pocket scientific calculators - it's worth getting a real one as well.

I bought my HP-21 shortly after i saw it in Machine Design magazine in 1976. From then on it became my constant companion until appx 1995 or so when it gave up the ghost and would no longer illuminate. Much later on I was overjoyed to find an e-version replica of my faithful pocket resource, though he was no longer needed after I retired from field work. Today I have switched to Android apps and regret that I cannot find a replica of this trusty device,,,,, and would like to ask IF THERE IS ONE (?) or one under development? All iOS products havre become too expensive and unreliable !

Many thanks for giving me the opportunity to use this RPN calculator. I bought my very first HP 21 C in 1972 when studying at Polytechnic School of Cameroon. 50 years later, I am still very happy and proud using RPN devices and programming Common LISP.

To me, the value of this app (and all the other RPN apps that I have) is the authenticity of them. Otherwise, there are a gazillion calculators with different sized displays out there with RPN. Instead of making the X view high visibility, why not enlarge the calculator itself to be full screen (even getting rid of the stack view optionally) Then I’ll go back to 5 stars again which otherwise this app absolutely deserves.

I’ve been using this app for a number of years and have been very satisfied and figured it was time I gave it a review. As an engineer, I loved my HP-21 and was sad when it finally died many moons ago. I searched and searched for a simple reverse Polish calculator app, but could never find a good one. This is a good one. A clean but elegant emulation of a classic design. Highly recommended.

I have an hp 21 that we purchased new and I've always loved it, not only for the RPN feature but for the simplicity. This is such a nice app for anyone familiar with the HP line plus it shows the stack. Highly recommend.

I bought an HP-21 during my third semester of college in 1976. At that time they were still teaching students how to use a slide rule. The app is a very good reproduction of the HP-21's look and functions/functionality. I has the functions I want and doesn't have a lot of functions that I don't use. It has a useful Help file.

Loved my 21; spent many hours with it in college. Doesn't charge anymore, but I still keep it around. This is an excellent reproduction. And then some.