HP 50g Graphing Calculator - Manual (Page 123)

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the HIST key: UNDO results from the keystroke sequence ‚¯, while CMD
results from the keystroke sequence „®.
To illustrate the use of UNDO, try the following exercise in algebraic (ALG)
mode: 5*4/3`. The UNDO command (‚¯) will
simply erase the result. The same exercise in RPN mode, will follow these
keystrokes: 5`4`*3`/. Using ‚¯ at this point
will undo the most recent operation (20/3), leaving the original terms back in
the stack:
To illustrate the use of CMD, let’s enter the following entries in ALG mode. Press
`
after each entry.
Next, use the CMD function („®) to show the four most recent commands
entered by the user, i.e.,
You can use the up and down arrow keys (—˜) to navigate through these
commands and highlight any of them that you want to entry anew. Once you
have selected the command to enter, press
@@@OK@@@.
The CMD function operates in the same fashion when the calculator is in RPN
mode, except that the list of commands only shows numbers or algebraics. It
does not show functions entered. For example, try the following exercise in RPN
mode:
5`2`3/*S
³S5*2` .
Pressing „® produces the following selection box: