User`s guide

trigger sample):
Pretrigger Sample Count ≤ Sample Count - 1
If any of the calculation functions are on (CALC:STAT ON), the pretrigger
count is further limited to 10,000 samples.
The CONFigure and MEASure? commands automatically set the pretrigger
sample count to "0".
The instrument sets the pretrigger sample count to "0" after a Factory
Reset ( *RST command) or a Preset (SYSTem:PRESet command).
It is recommended that all triggered measurements be made using an
appropriate fixed manual range. That is, turn autorange off
(SENSe:<function>:RANGe:AUTO OFF), or set a fixed range using the
SENSe:<function>:RANGe, CONFigure, or MEASure command.