HP 35s Scientific Calculator - Manual (Page 231)

Programming Techniques 14-21
The Indirect Address, (I) and (J)
Many functions that use A through Z (as variables or labels) can use (I) or (J) to refer
to A through Z (variables or labels) or statistics registers indirectly. The function (I) or
(J) uses the value in variable I to J to determine which variable, label, or register to
address. The following table shows how.
STO I INPUT I DSE I
RCL I VIEW I ISG I
STO +,–, Ч ,ч I ∫ FN d I x < > I
RCL +,–, Ч ,ч I SOLVE I