User`s guide

Description
This command selects the trigger source for measurements. The instrument
will accept a software (bus) command, an immediate (continuous) trigger, or
an external TTL trigger pulse. The 34411A and L4411A will also accept a
trigger level.
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.