User`s guide

Remarks
The actual trigger event occurs on either the rising edge (if POS is
selected) or the falling edge (if NEG is selected) of the trigger signal. See
Ext Trig Input for further information.
The instrument selects a negative slope after a Factory Reset (*RST
command) or an Instrument 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.