Scientific Calculator Keyboard Challenge

[bhtooefr]

Here's 24 keys, in a layout I mocked up for a 41-compatible watch idea I had:



So, the UI is somewhat menu-driven - SET (settings, including ASN, submenus for number format, trig representation, and the clock), TRG (ASIN, ACOS, ATAN, P→R, R→P), MTH (x^2, 10^x, LN, e^x, %), STT (Σ+, Σ-, CLΣ), PRG (LBL, GTO, ISG, RTN, BEEP), FLG (SF, CF, FS?), and CMP (X=Y?, X≤Y?, X>Y?, X=0?, FS?) are menus.

Now, when I mocked that up, the idea I had was to have four extra buttons (total of 28) for On (which would not actually turn it on - it would act as a mode selector ala the mode selector on my Casio CA53W-1, switching between watch (CLOCK), calculator, and stopwatch (SW), with using any functionality at the calculator or stopwatch causing it to reset to watch on the next press), User, Prog, and Alpha. However, to get it down to 25 keys... it's doable to stuff USER in the SET menu, PROG in the PRG menu, and then make Alpha a Shift-On.

Alpha, by the way, is implemented through the rather annoying system of cell phone keypad entry, but hey, it's better than 42S entry.

I also had the idea of multiple display modes, so you could have a fully backwards compatible display like this:



Or multiple visible stack levels like this:



(the menu options at the bottom look like crap, I'll admit)