GO-21 SciRPN

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.

I used an HP-21 calculator in college back in the late 70's and early 80's. The rectangular-to-polar and polar-to-rectangular conversions were a lifesaver for an engineering student back then. This app is a great update to the original. The built-in help is excellent too. The ability to "commify" numbers is my favorite added feature. The developer is also very responsive.

I was 18 when the HP-21 was released but did not buy one until years later when I was in College (I was in the US Army until age 21). This iPhone version is delightful to use and it works very well on my iTouch with the latest OS and indeed fast app switching works well. The display and buttons are easy to see and use. Swiping to see the entire stack is useful. Thanks for writing this app.

A Classic! Just like my old HP-21 -- even to the realistic LED display. I have at least a dozen RPN calculators (both real and as iPhone Apps). Many are much more complex with lots of advanced features. But, if you are a RPN user, this HP-21 App is just perfect for going to for quick straight forward calculations. It has become my most used calculator.