Four?! Why not more?

[Massimo Gnerucci]

(06-14-2021 08:45 PM)OlidaBel Wrote:  

(06-14-2021 02:55 AM)rprosperi Wrote:  Well, after X, Y, Z and T for TOP were used, there was no more room; you can't have a register past the top, there's just no room left. :)

X,Y,Z,T,C
C: ceiling.

(busy digging the HP-15C manual. some archeology :-) )

Well then why not X, Y, Z, T, O (over the top)? :D