Full emulation of the classic and ground breaking HP-67 calculator produced back in the early 70's. An amazing device developed by Hewlett Packard which is still very useful.

Note: newer Galaxy 8 Plus (and similar phones) have "full screen" modes that you can change in Settings/Screen/Full Screen that can be changed on per-app basis. Insure this mode is disabled for the HP-67 app. It will fix issues with button presses being offset from buttons.