Command
:CALCulate<Ch>:PARameter<Tr>:SELect
This command sets the selected trace as active trace. Use :DISP:WIND:ACT to activate the channel.
Ana.WriteString ":CALC1:PAR1:SEL", True
:CALC:PAR:COUN
:DISP:WIND:ACT
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SCPI.CALCULATE(Ch).PARAMETER(Tr).SELECT