Wind the knob till it stops....
Count the number of turns or part turns it takes to get it to the other end stop.....
Halve that number exactly......
Turn the knob back that number of turns......
Hey presto, your at zero for that plain, repeat for other elavation, jobs a good'un
I always then roughly zero the scope to the rifle by using shims to either shift the POI left or right, or up and down, then and only then do I use the elevation knobs to do the final zero
