HP 83751A Programming Manual page 181

SWEep:MARKer:STATe
Sets and queries the state of marker sweep. When this state is ON, the
frequency sweep limits are taken to be from position of marker 1 to position
of marker 2. If marker 1 was previously set to be greater than marker 2, their
values will be permanently interchanged so that the instrument sweeps up in
frequency.
Setting SWEep:MARKer:STATe to ON will turn marker 1 and marker 2 on.
*RST value is 0.
SWEep:MARKer:XFER
This transfers the values of marker 1 and marker 2 frequencies into
FREQ:START and FREQ:STOP, respectively. If marker 1 was previously set
to be greater than marker 2, their values will be interchanged so that the
instrument sweeps up in frequency.
Programming Commands
Sweep Subsystem
2-75