HP 33s - Manual (Page 105)

Entering and Evaluating Equations 6–13
„ To change the number, type the new number and press g . This new
number writes over the old value in the X–register. You can enter a number as
a fraction if you want. If you need to calculate a number, use normal
keyboard calculations, then press
g . For example, you can press 2
‘ 5
g .
„ To calculate with the displayed number, press ‘ before
typing another number.
„ To cancel the prompt, press ‡ . The current value for the variable
remains in the X–register. If you press ‡ during digit entry, it clears the
number to zero. Press ‡ again to cancel the prompt.
„ To display digits hidden by the prompt, press |  .
Each prompt puts the variable value in the X–register and disables stack lift. If
you type a number at the prompt, it replaces the value in the X–register. When you
press
g , stack lift is enabled, so the value is retained on the stack.
The Syntax of Equations
Equations follow certain conventions that determine how they're evaluated:
„ How operators interact.
„ What functions are valid in equations.
„ How equations are checked for syntax errors.
Operator Precedence
Operators in an equation are processed in a certain order that makes the
evaluation logical and predictable: