So you calibrated the SA by using a stable source (the SG504?) and a
Boonton 4210-4B to about +/-0.15dB and then used the SA to evaluate
the two different SG504 leveling head designs, right?
Why not just use the Boonton 4210-4B directly without the SA?
Do we have any details about how Tektronix determined the performance
of the SG504? The specifications say:
"Flatness is referenced to the NBS corrections of Tektronix standards.
Uncertainties of the NBS are not included in this specification."
Which I take to mean Tektronix sent their golden power meter or other
measuring instrument off to NBS and it was returned with a calibration