TO THE LEFT:
Here I am using the fret-slotting miter box, along with the fret scale template (which has indexing notches on one side for the 13.75" soprano uke scale I am using for this project), to cut the fret slots with a Japanese pull saw.
First, I stick the bloodwood fretboard to the metal fret scale template with double-stick tape, and then slide the template into the miter box. There is an indexing pin in the front inside wall of the box, just to the left of the cutting area. (I have already adjusted the bearings for the desired depth of cut.) I place the template so the pin engages the first notch of the template (which represents the nut end of the fretboard) and saw my first slot. Then I slide the template to the next notch and I saw that slot --- that cut will be the first fret. And I just continue on from there, until all 13 slots have been sawn.
The result: an accurately slotted fretboard. After I remove the fretboard from the template, I saw all the way through that very first slot (which was the nut slot).
TO THE RIGHT IS THE RESULT. (Those slots at the bottom end of the board to the right are where I was testing out my adjustments to the bearings for the depth of cut.)