Perhaps the best of the 15c clones

This hasnt been updated in ages but it remains a great 15c calculator. The best RPN calculator Of the dozens Ive tried. Ive used it for years on my iPads and iPhones, up to iPhone 6 and iPad Air 2.

Havent encountered any issues, but obviously it is very difficult to exercise the majority of the features this has.

It has a great built in user manual which obviously helps with some of the more advanced functionality, but if you are familiar with RPN its more nascent features are intuitive.

I havent given it 5 stars as it hasnt been optimized for the different aspect ratios of the newer iPhones. Doesnt affect functionality, though.

The default key click sound can be turned off in the iOS Settings; some people wont know to do that and can be put off by the clicks.

Cryolathe about HP 15C Calculator, v2.0.1