RPN 28x Calc

I grew up using a real HP32, so perhaps I’m biased towards this interface, but I love using this calculator. It provides the best balance between being a traditional RPN calculator and maximizing the benefits of the smartphone I’ve seen. Most of the straight HP calculator emulators use the original display, which has, at most, 4 visible numbers in the stack. Why? That’s a silly limitation on a smartphone. This app also lets you do actual drag and drop on the stack so you don’t need to be adept at ROLL and ROLLD commands. Bonus binary conversions, etc. Most RPN calcs that aren’t based on an original HP architecture just don’t implement RPN well —including the “new” HP Prime (which I own and don’t consider a traditional HP). I encourage you to skim the manual. This app has so many features that you can get lost. I use, at most, 10% of the features, and would not have found my favorites by randomly pushing buttons.

My electrical engineer dad gave me his HP 45 to use in middle school when he no longer needed it. As a birthday present from Service Merchandise, my parents gave me a new HP 41CV. It carried me through High School, College and Grad school. I still have it. The 41CV is in a safe place. The HP 28c/s came out in college but I couldn’t justify the cost. I have most of the HP emulators on my iPhone. This is by far my favorite. It utilizes the screen better then any other HP calculator app. It doesn’t over load the screen keys with too much information. It allows the alternative key functions to by swiped to become active. The user can select more easily the key needed. The colors of keys and output display are contrasting which makes using the calculator a joy. Haptic feed back is awesome too. Finally, a right swipe brings up a blank keyboard area you can populate with custom keys/variables/functions. This is the RPN calculator app HP would release. It is better then a physical calculator. It does not try to be a physical calculator it uses the strength of an iPhone/iPad screen to make it more usable and user friendly. You can’t go wrong with this app. Keep up the great work.

I use this calculator a lot when breadboarding circuits, and I’ve added a whole bunch of custom buttons tied to functions that calculate values related to the ICs I’m using, eg. voltage regulator feedback resistors, current setting resistors, “quick” filters, inductor/capacitor ripple, type II and III compensators, etc. It is a little marvel. Somehow, this button-based RPN interface really makes it work on a touch screen, whereas various other “mobile” interfaces that try and exploit fancier controls fall way short of the promise. This one has just the right mix of plain “buttonery” and screen gestures. I like it better than the thing it’s emulating. I know, what a travesty, but there you go. If only phone batteries lasted as long as calculator batteries. But as far as this app goes, it seems to do everything right and is a battery-miser. The rest is on Apple to improve :)