Ups, you do not have to measure the thickness of the vertical rail.
http://homepage.mac.com/hindenhaag/filechute/LRS-M1.tif I have added some signs to understand it better.
For LRS just add the measurement O + H. Actually we need the lens axis with camera pointing down -90° directly to the rotation center of the rotator. The easiest way is to measure O + H with a ruler. Mount the camera to the upper rail, the slide the lower rail to LRS and fix the clamp. Now the lens axis should be very close to rotation center of the rotator.
Now add Smooth's "hacksaw method" as I already described below to fine tune the LRS.
Actually there are two ways to get near the LRS: measurement of O + H, or the "viewfinder method". Viewfinder method: fix camera to upper rail, set pitch= movements up and down to -90° on upper rotator. Now the lens points down to the lower rail. Now open up the LR-clamp, look through the viewfinder and slide the lower rail into place till you see the center of the rotator in the center of the viewfinder. If I remember well, Demon is shooting with a compact camera. So may be he has a "Cross Hair" in the center of his viewfinder. Then he will use this mark to place it on top of the rotation center of the rotator. Let us call it RC.
With NN3, NN5, you could use the logos center on top of the rotator and before this the fixing screw of lower rail to rotator to center it easily to the center of the viewfinder. With M1 Series, there is no logo to center to. The only possibility to center to are the marks on top of the lower rail clamp besides the lower rail. This is a lot more tricky. Because of this, Nick and I advised to measure the "theoretical LRS" of O + H.
Anyway, to correct "faults in the camera lens system" use the hacksaw method to fine tune LRS.
@bbc597: Did I explain it in the right way to understand what we are talking about?
Feel free to ask.
Can you comment on the "hacksaw method" using the M1 clamp? With the M1 clamp being larger, you cannot see the rounded edges of the rotator.