HP20b - Switch between RPN and Algebraic

The Mode menu allows you to customize the calculator. To access the Mode menu, press [Shift][Mode]. Press [Up Arrow] or [Down Arrow] repeatedly to scroll through the menu starting with FIX=2 (the number of digits displayed to the right of the decimal point). Once an item is displayed, press [INPUT] key to cycle through the other options for that setting. To exit the Mode menu, press [ON/CE] key once.

Chain, Algebraic, or RPN operation mode.  The HP20b default mode is set to Chain operation mode. Pressing [INPUT] key to cycles through these options.

HP 20b Keyboard & Display Reference » HP 20 b Switch to Algebraic Mode · HP 20 b Switch to Chain Mode · HP 20 b Switch to RPN Mode ·