Version: 1.1.2LXVII is a faithful simulation, but not exact emulator, of the HP-67. It has the same number memory registers and program steps as the original.
Operating System: Mac OS X
The stack depth is the same (4 cells), the button and prefix key layout is also the same, (which unfortunately makes its on-screen footprint a bit larger than it was intended) it displays the same key-codes per program step, it even has a slider switch for selecting between user and program mode.
The impetus for keeping that level of compatibility was to give the owner of an HP-67 the ability to immediately use the application without needing to worry about differences from what he or she is used to.
New features were created with the intent that they extend existing features in a matter that was compatible with existing behavior.