Command
:CALCulate<Ch>[:SELected]:MARKer<Mk>:ACTivate
This command sets as active marker.
Ana.WriteString ":CALC1:MARK1:ACT", True
:CALC:MARK
Marker > Marker 1 to Marker 9, Reference Marker
SCPI.CALCULATE(Ch).SELECTED.MARKER(Mk).ACTIVATE