Calculator technique for evaluating Limits ( Differential Calculus) using Casio 991 es/570 es. To evaluate a limit as x approaches a certain value "a", substitute a number to "a" that is very close to "a". For example: x approaches 1, let x= 0.99999 or 1.0001 ; x approaches 2, let x=1.9999 or 2.0001; x approaches 0, let x=0.0001; x approaches infinity, let x= 999999 IMPORTANT: Set the calculator to radian mode (Shift-Mode-Rad) for limits involving trigonometric functions.