The LAST X register, a separate memory register, preserves the value that was last in the display before execution of a numeric operation*. Pressing g LSTx (LAST X) places a copy of the contents of the LAST X register into the display(X-register). For example:
|---------> lost
T t ----------> t -| |-------> z
Z z ----------> z ---| |-----> y
Y y ----------> y -----| |---> 16
X 4 --------|-> 16 -------| |-> 4
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Keys: g x^2 | g LSTx |
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LAST X: / |-> 4 ---------|-> 4
The LSTx feature saves you from having to re-enter numbers you want to use again. It can also assist you in error recovery, such as executing the wrong function or keying in the wrong number.