"If too high, you must saw (with fine-gauged saws) or file (with nut-files) the slots down, a few strokes at a time, until they are right. Drat, sometimes that single extra stroke was one too many! In cutting the slot, the best way to proceed when you start to get close to the desired depth is to check it after each tool stroke. Make sure to angle your tool-stroke to yield a slot floor that is inclined relative to the fretboard but just about the same as the angle of the headstock or flatter– certainly not steeper."