HP 35s Scientific Calculator - Manual (Page 179)

Statistical Operations 12-13
You can load a statistics register with a summation by storing the number (-27
through -32) of the register you want in I or J and then storing the summation (value

7
or
A
). Similarly, you can press  
7
or
A
(or 

7
or
A
) to view (or recall)a register value — the display is labeled with
the register name. The SUMS menu contains functions for recalling the register
values. See "Indirectly Addressing Variables and Labels" in chapter 14 for more
information.