VSWR Meter measurement

I am using the following steps to measure Low VSWR,

1. Move the probe along the slotted line to get maximum deflection in

VSWR meter.
2. Adjust the VSWR meter gain control knob or variable attenuator

until the meter indicates 1.0
on normal VSWR scale.
3. Keep all the control knob as it is move the probe to next minimum

position.
4. Read the VSWR on scale.

Can anybody explain, why we are using first three steps instead
of measuring direct VSWR reading from VSWR meter ?


**broken link removed**

It is because you are measuring a ratio.

You set the first point to 1.0 on the meter and then the second point is measured relative to the first.