HP ProBook Notebook PC User Guide - Windows XP

Using an optional external numeric keypad
Keys on most external numeric keypads function differently according to whether num lock is on or off.
(Num lock is turned off at the factory.) For example:
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When num lock is on, most keypad keys type numbers.
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When num lock is off, most keypad keys function like the arrow, page up, or page down keys.
When num lock on an external keypad is turned on, the num lock light on the computer is turned on.
When num lock on an external keypad is turned off, the num lock light on the computer is turned off.
To turn num lock on or off on an external keypad as you work:
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Press the num lk key on the external keypad, not on the computer.
Using an optional external numeric keypad 45