I really don’t think there is any need to be that precise, by that I mean it needs to balanced but just by look and feel, no need for taking measurements, besides mounds guide better when slightly loaded on the east side and also back heavy, if you have it too well balanced you may get it flipping back and fourth inbetween teeth on the worm gear, and nobody wants that..
Something to consider though, it is best to have more weight higher up the weight shaft rather than less lower down, as this reduces the work the mount has to do...I will explain
The effort required by the mount to change the movement of an axis is determined by the moment of inertia. The moment of inertia varies as the square of the distance to the counterweights.
Consider two different configurations. The first one uses 10 lb of counterweights 10" down the shaft, and the second one uses 5 lb of counterweights 20" down the shaft. They will both balance the same, but the second one has twice the moment of inertia as the first. So any time the mount needs to start tracking, stop tracking, or make a guide correction, it will have to work twice as hard.
To get the best imaging performance out of the mount, you want the counterweights as close to the axis as possible, even if it means the mount is carrying more weight. As long as the load is balanced, reducing the moment of inertia more than offsets any negative effects of the extra counterweights. HTH..