HP 30b Business Professional Calculator - Manual (Page 34)

Mathematical Calculations 26
In RPN mode, the
%
key calculates x % of the number on Level 2 of the stack, when x is
the number on Level 1 of the stack. It does not modify the number on Level 2 of the stack, and
thus allows you to perform addition or subtraction after pressing
%
to add or subtract x %
from the number.
For example,
200I25%
returns 50, but 200 is still on Level
2 of the stack, and pressing
-
returns 150, or 200-25%.