RPN Anywhere

Functionally, this is a pretty competent RPN calculator. The design isn't trying to directly copy an old HP interface and it's the better for it. On iOS, that's essentially the end of the story. It works.On WatchOS, the user interface design has a number of major inconsistencies with standard UI patterns:The watch app is organized as a single screen with two trays at the top and bottom. The trays are accessed exclusively via touch. The stack is in the top tray and advanced functions are in the bottom tray. This is quite different from most software for the Watch, which generally use sliding cards to access things which don't fit on one screen.The lower tray, sensibly enough, is accessed by swiping upwards anywhere on the bottom edge of the display and dismissed by swiping downwards.The upper tray, on the other hand, is accessed by swiping down from the right half of the top edge of the display. There does not appear to be any function assigned to the left half of the display. The tray is dismissed by swiping upwards, but a full row of space in the stack is dedicated to a large "back" button which duplicates this for no discernible reason.This arrangement simply isn't very good. Every Watch includes a hardware control for vertical movement and it's not used in any way despite the use of vertical movement for navigation. The touch controls are implemented strangely. The end result feels very non-native, is fiddly to use, and generally lacks polish.

If you're looking for a simple RPN calc that features keyboard input that makes sense (and/of is customizable) compared to the default calculator (in RPN mode) then get this calc.The only things I wish it had are a few more GUI keys. An EE key in "basic" mode would be nice, and more stack control keys (Roll up/down, Drop) in both modes for when you want to be lazy and only use the mouse. The "scientific" mode already features an EE key and thanks to the programming function I added the stack control keys as programs. Programs appear as keys below the display starting at the left, I added a couple blank programs with spaces for titles to move my stack control keys above the numeric keys. It's almost perfect!

Though I am eager to give this app 5 stars, I bought this for use on my Series5 watch but find that there is a bug with WatchOS 7.1 which won't let me swipe to get back to main from the function screens. Unfortunately, the app support page is not in English, so I don't know if there's a workaround. So why did I give it 4 stars even though it has a debilitating bug? It is unapologetically RPN. The layout and functionality isn't perfect; but it is the most practical design I have seen for writing useful scientific/engineering programs on an iOS device. The layout and functionality on an iPad is stellar. I will definitely keep this app hoping that the watch bug gets fixed. It is very much worth it's price.