HP 54645A User's And Service Manual page 164

Making Measurements with HP 54645A/D Oscilloscopes
To make cursor measurements
Use the Entry knob to move the cursors. You can toggle the active cursor
by pressing the cursor key while in the cursors menu.
Cursor measurements are not bound to the edge of the screen. If you set a
cursor, then pan and zoom the waveform until that cursor is off the screen,
when you set the other cursor, the measurement will still be accurate.
Figure 5-16
Cursors Measure Pulse Widths other than 50% Points
Figure 5-17
Cursors Measure Frequency of Pulse Ringing
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