The references in another topic mentioning the Commodore SR7919 and Commodore PR100 - which were my first two calculators and it got my memory banks working.

I knew the PR100 inside out, one undocumented feature relates to the 9M function which would apply the same arithmetic function to each of it's ten memories - yes ten not nine memories, eg 15 M+ 9M would add 15 to each of the ten memories.

The PR100 also had an X <> M function. This would exchange the number on the screen or the X register with one of the ten memories chosen by the user.

The undocumented feature was that if you combined X <> M with the 9M function it would move the number on the screen (X register) into the contents of memory 0 , memory 0 into memory 1 , memory 1 into memory 2 etc until memory 8 moved into memory 9 and memory 9's contents were displayed onto the Screen.

Oh the memories .......

Nigel

Commodore had a range of amazing calculators, especially the button monsters or the x190 series, which offered a broad range of interesting functions. My 4190 is never out of reach at home, and I also like the PR100 very much. Still waiting for a good offer on a 9190 :-).