HP 1652B Getting Started page 21

Keypad
The keypad has keys for entering data as well as the RUN and STOP
keys (for acquiring waveform data). When entering numeric data, use
the CHS key to change the sign of the number. When entering
patterns, the DON'T CARE key enters an X ("don't care") in place of a
regular digit. Pressing CLEAR ENTRY replaces the entry with the
default value.
Summary
Now that you are acquainted with the front panel organization, you will
be able to decide where you want to go next. If you are just starting to
learn logic analysis, you should read this entire guide. If you are
experienced in logic analysis, you should continue to read chapter 3 to
become more familiar with the operation of the front panel before you
turn to the reference manual.
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Getting to Know the Front Panel
2-4