HP 54501A Programming Reference Manual page 207

All voltage
values are returned
in volts. Returned
voltage values are
measured with zero
volts as
the reference.
The
value returned for
the
VDELTA?
query
is
the difference between
VMarker
1
and VMarker
2
in
volts.
All
time values
are returned in
seconds.
Returned time values are
measured with the trigger point (time
0)
as
the reference. The value
returned for
TDELTA?
is
the time difference between the stop
and start
markers.
Measurements are made on the
displayed
wavefonn(s) specified by
the
SOURCE
command. The
SOURCE
command
allows two sources
to be
specified. When two
sources
are specified,
VMarker
1 is assigned
to the
first
specified
source and VMarker
2 is
assigned to the second
specified
source.
VDELTA
is the only measurement that
uses
two
sources.
Most
measurements can only be made on
a
single
source.
If
one
of
these
measurements
is made with two
sources
specified, the measurement is
made on
the first source specified.
More information
about measurement algorithms can be found in
Appendix
A.
If
the
horizontal scaling
is questionable, an "error
11" is placed in the error
queue.
In this case the
value returned
is
the most accurate that can be
made using the current scaling.
You
might be able
to obtain
a
more
accurate measurement
by rescaling the horizontal to obtain more data
points on the
edge.
Refer
to figure 14-1 for the syntax diagram
of
the
Measure
subsystem
commands.
HP
54501A
Programming
Measure Subsystem
14-3