Agilent Technologies Infiniium 8000A Programmer's Reference Manual page 529

Command
<source> {ALL | CHANnel<N> | FUNCtion<N> | WMEMory<N>}
<N> s an integer, 1 - 4.
<upper_pct>
<middle_pct>
<lower_pct> An integer, - 25 to 125.
<upper_volts>
<middle_volts>
<lower_volts> A real number specifying voltage.
:MEASure:DEFine THResholds,STANdard,<source>
:MEASure:DEFine TResholds,PERCent,<upper_pct>,
<middle_pct>,<lower_pct>,<source>
:MEASure:DEFine THResholds,VOLTage,<upper_volts>,
<middle_volts>,<lower_volts>,<source>
Measure Commands
DEFine
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