HP-25 statistics weirdness

[John Garza (3665)]

Ever notice the HP-25 does not accumulate the y^2 value in a stat register? Makes things like computing r^2 for linear regression a chore as you have to account for it in your code on data entry. Also, RCL Sigma+ is not allowed - making our fearless pilot Mr. Sweeny hit a couple of extra keys - not to mention having to remember where SigmaX and SigmaY are stored.

Doing a little research, I found the HP-25 is unique in this. It's predecessor, the HP-55 has both y^2 and RCL Sigma+, and so does it's successors, the HP29C and the HP-33E/C. The HP-27 has y^2 but lacks RCL Sigma+.

I presume all this weirdness is due to space imitations? And yet the 25 has percentage and NOP ?

-J