Every cutting tool has a kerf — the amount of material that the tool itself removes in the cutting process. With a table saw, it tends to be large, like 1/8″. The laser-cutter has a small — but significant kerf.
I cut a 1/4″ notch and then used the calipers to determine that I have a 2/100″ kerf when cutting 3/8″ material at 8/100/500 (speed/power/frequency).
I then cut a 1/4″ groove and several notched cutouts, increasing the amount of material by incremental values. At 4/100″, (double the .02 measurement), the fit is perfect. 3/100″ is a little loose and 5/100″ won’t fit.
I’m glad I was a high-school mathlete.