Now available on iTunes: HP Prime Graphing Calculator iOS app

[Kevin]

This excellent emulator works well on both my iPad 3 and iPhone 6* but when I try and install it via iTunes on the old iPhone 4 (IOS 7), I get no visible keyboard appear.
The keys positions if guessed at are responsive to touch but I'd like to actually see them!

Any ideas?

*The iPhone6 emulator is so fast that a huge series (see attachment) that takes around 4 seconds on the real calculator is finished in half that time on the phone.