Try this on a 15C: Hold down "-" while hitting "ON" (this will clear all of your memory). With Pr Error displayed, turn the calc off. Turn it on again, press "4" and turn it off again. Now hold down the square root key (upper left) while turning it on, and turn it back off, 5 times. Display should read "b 0 0". Hit "+". Some program runs, and the display reads "A 0 0". Now press and hold "+" or "-" for about 5 seconds. Display reads "null" like a 41 would. I don't know what good any of this is, but it's weird.

I tend to think of my preoccupation with HP calculators as a point of distinction, a matter of pride, a highly specialized hobby. However, I'm beginning to wonder . . .

It appears that the "hard reset" (ON-) is not necessary. Also, the same result can be acheived by pressing (ON-y^x) 5 times. Other models/values yeild strange display results but never enter this strange "b 0 0" mode.

Mark Hardman (led)

it appears to be activating the matrix mode, for unknown reasons. the a......0.0 and b......0.0 are normal matrix operation displays, as is the null indicator. other voyagers lack this feature and give different results.

Looks like you've stumbled upon the window into the machine's guts...

See http://www.jlw.com/~woolsey/15Cnotes.html for details.