HP 16500C - Manual (Page 60)

Skew Adjustment
You can modify the skew or timing deviation between modules within
the intermodule measurement. This allows you to compensate for any
known delay of the system under test, or to compare two signals by
first removing any displayed skew between the signal channels.
Skew adjustments can correct module delays to within 2 ns of other
modules. Note that the module or channel that is used as the trigger is
normally the reference channel, and adjustments are normally made
to deskew the nonreference channels.
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