I use an adjustable bow stringer with leather straps on each end. Once the bow is at desired draw length and close to desired weight.
I will then place it back on the tiller tree, draw it to desired length. At this point I place a string line on the knock point on the bow string
and then pull the string tight to the desired knock point on the upper limb and then make the mark.
For the lower limb, I do the same, but I have found by doing this.... The lower limb knock angle will be ''slightly'' more than the upper due to the fact that I shoot with one finger above, and two fingers below the arrow knock. After I have made the marks, I remove the bow and cut the grooves, then I will make a new string for the bow.
Maybe I am over thinking it, but this is how I have got better result, regardless of the bow over all length.
one can not find the exact string angle unless you know the draw length and the radius arc of the limb.
With that said the exact string angle can be found for a specific bow once the limbs are near perfect tiller.
Any replies are welcomed.