HP 83751A Programming Manual page 134

Programming Commands
Frequency Subsystem
Sets and queries the CW frequency. This does not change the sweptkw mode
switch.
*RST value is (MAX + MIN)/2 See FREQ:CENTER for more information.
FREQuency[:CW]:AUTO and
FREQuency[:FIXed]:AUTO
Query Syntax
Couples the CW frequency to the center frequency. Explicitly setting a value
for FREQ:CW set FREQ: CW AUTO to OFF.
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