Tuning knobs A, B, and C are identical. They are used to coarse tune the selected frequency in
the window (bisected by a hairline). When rf tuning with the meter, they are adjusted for minimum
reflected power and zero phase through the band-pass filter. The lock knobs are each turned
counterclockwise to unlock the tuning knobs and turned clockwise finger tight to lock the tuning
knobs when tuning is completed.