From my deep & extensive research of about half an hour, it would appear that the HP35 in 1972 and all subsequent handhelds up until the HP10C in 1981 had their four function keys in the order / x + -. Suddenly there's a switch to + - x /.
1) Where did this "odd" / x + - come from? It seems natural, to me, to have the + at the lower corner since it's the most likely to be used.
2) The desktops before, during & after these nine years all had + - x /.
3) Surely there must have been a hoo-har in '81 when, after nearly a decade, a fundamental and, by now, "standard" layout was completely altered? Something akin, I'd imagine, to suddenly having a little piddly enter key hidden away somewhere. What? They have? Oh sorry, didn't notice!
I cannot find any reference to this in any history. Any info, reminiscences, comments?