There are a few different ways to set the elevation knob on a Garand floating around. Before setting this you will first need to determine what the correct amount of clicks is for your rifle to hit the X ring.
This is how I do it:
1. Run the rear sight all the way down.
2. Loosen the elevation knob screw.
3. Continue turning the knob down until you reach your desired hashmark.
4. Continue turning the knob down counting to your desired number of clicks.
5. Tighten the elevation screw without moving the knob.
6. Turn the knob up verifying that when you have reached the number of clicks you were looking for it stops at the desired hashmark.
7. Run the rear sight all the way up and tighten the elevation knob screw all the way.
8. Return the sight to zero and go shoot in a local match.
A fair amount of competitors don’t bother with this and just count clicks. It can be a useful practice as it helps you verify at a glance you are at the right elevation. However, on the other hand, I have had the rear sight loosen up on me and cause the elevation to appear correct but the number of clicks had drifted. Best practice is probably “trust but verify” and set your your elevation knob to the right hashmark but verify from time to time, at least before each match. It is also a good idea to write your elevation and windage down on a card and place it in your stock.