Agilent Technologies Infiniium 8000A, Programmer'S Reference Manual

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Data Acquisition
When data is acquired using the DIGitize command, the data is placed
in the channel or function memory of the specified source. After the
DIGitize command executes, the oscilloscope is stopped. If the
oscilloscope is restarted by your program or from the front panel, the
data acquired with the DIGitize command is overwritten.
You can query the preamble, elements of the preamble, or waveform data
while the oscilloscope is running, but the data will reflect only the current
acquisition, and subsequent queries will not reflect consistent data. For
example, if the oscilloscope is running and you query the X origin, the
data is queried in a separate command, it is likely that the first point in
the data will have a different time than that of the X origin. This is due
to data acquisitions that may have occurred between the queries. For
this reason, Agilent Technologies does not recommend this mode of
operation. Instead, you should use the DIGitize command to stop the
oscilloscope so that all subsequent queries will be consistent.
Waveform Data and Preamble
The waveform record consists of two parts: the preamble and the
waveform data. The waveform data is the actual sampled data acquired
for the specified source. The preamble contains the information for
interpreting the waveform data, including the number of points
acquired, the format of the acquired data, and the type of acquired data.
The preamble also contains the X and Y increments, origins, and
references for the acquired data.
The values in the preamble are set when you execute the DIGitize
command. The preamble values are based on the current settings of the
oscilloscope’s controls.
Function and channel data are volatile and must be read following a DIGgitize
command or the data will be lost when the oscilloscope is turned off.