Old Sherwood tube tuner

I have a old old Sherwood tube tuner model S-3000 IV. There is a level set screw on the back, what does it do?
Any feed back on this old timer?
As I remember, that adjusts the output. Idea being you could have the tuner and turntable (regardless of cartridge) match exactly when you selected back and forth.

If the tubes are in good shape and alignment is correct that is a very nice sounding piece.
Albert is right that they sound good but the one I had years ago drifted like survivors of the titanic!
Good to see ya out and about tonight Albert. Check out your cryo'd Hubbell thread and tell me what ya think? :)