HP 35s User Manual page 179

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
A A
7  7 
or ). Similarly, you can press or (or
A
7
or ) 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.
12-13
Statistical Operations