HP 54645A User's And Service Manual page 172

To measure the duty cycle
To measure the pulse widths
Figure 5-24
Positive Width Measurement on HP 54645D Digital Channels
Making Measurements with HP 54645A/D Oscilloscopes
Press Next Menu until you find the Duty Cy softkey, and press it.
To measure the positive pulse width, press Next Menu until you
1
find the +Width softkey, and press it.
To measure the negative pulse width, press Next Menu until you
2
find the -Width softkey, and press it.
To make time measurements automatically
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