Some parts I can estimate, then stand back and see if more needs removal. What I'm doing on that lower section is driving skinny
4 FOOT survey stakes on the opposite side of the hedge about 1 inch out from it. Then I'm
stringing a line, and adjusting the line by sight looking at a couple of angles and nudging it till it looks right.
Then I'm placing my hedge shear bar just beneath the line holding the blade level to avoid cutting the string line.
This lower section is the only area where I'm using the string line. Other areas like the driveway where the surface is flat and consistent where I walk.
I have to admit...I leave the shearing and hedging to the hedge guy, but shrubs and specimen trees, fruit trees...I can get into my zen on a day of pruning.
The reason I enjoy normal pruning of thinning and directing, and some fruit trees, is that it's opposite of shearing.
I've always described hedges and shearing as something that controls people. Once a hedge is set into motion and formed, it mandates that someone must prune it, and it must be done at certain intervals. And it sets it's direction, which is almost static to outward, excluding renovations.
For other pruning, a man or woman can continually determine the direction of growth and modify the form and density. Given time, a canopy can be shifted over many feet, leaned to the left, raised, wrapped around a corner, or be allowed to expand evenly in all directions with thinning as desired.