On an iPhone XS Max, with iOS 13.2.3, after loading it, this calc crashes systematically on hitting any key - in short, it's useless.---The developer fixed the problem. Now the app is fine.

The emulator is too unstable to be useful for programming. Exiting and re-opening of the app erases all programs already written. On first use, or after memory purge, the number of programming registers sets out with the expected maximum (319) for this calculator. However, any entries made in programming mode inexplicably reduce this back to 49 registers - or less (depending on the number of program lines entered at that stage). The app comes loaded with advanced modules, such as 'CX TIME' and 'CX EXT FCN'. However, when running programs, the calculator is quite slow, even compared to the actual HP-41CX calculator from the 1980's. The stopwatch function does not clock actual real time and is thus of no use. For aficionados, the app's calculator image is only vaguely reminiscent of the original.Overall, this app is poorly put together and effectively useless for programming. Switching to the excellent 'i41CX' app instead (available from the Apple App Store) provides for a much superior user experience.

I loved it while it worked but apparently is incompatible with IOS 13.2 and app support no longer works. It opens but any further attempts to use it resulted in a return to the IOS home screen. Was my favorite but I can no longer recommendUPDATE: downloaded the latest update and it’s my favorite again. IOS 14.4 works great!

In February 2021 the app was fixed and it works like a charm again. This was a favorite app until IOS 13 when it quit working. I am thrilled to have it back.The GUI is no longer the accurate visual reproduction of if the original HP layout; however the functionality is back! Today I Snoopy-danced with joy.