With the palmtop off, hold down [Esc] and press [On]. The palmtop enters its ROM-based self-test mode. (Warning! Do NOT run the Plug-in Card test on a flash card - it will destroy data! This test is meant for older SRAM cards only!)

Cursor down to the Display test, then...

For HP 95LX, 100LX and 200LX:

Press [Enter] 14 times to step through the display modes, and you will see a limerick about a caveman.

For 100LX and 200LX:

Press [Ctrl]+[Enter], then hold down [Alt] while pressing [Enter] 13 times. You will see a cryptic poem, presumably about troubles the HP developers went through.

For 200LX:

Press [Ctrl]+[Enter], then hold down [Shift] while pressing [Enter] 13 times. You will see a poem about Jaguar, Cougar and Felix (the codenames for the 95LX, 100LX and 200LX).