i must've already posted 2 or 3 threads about this, but i just dont get it. i have an existing neck that i need to slot. it has a nut (precision) already, so using a caliper is not really possible. i'd use a ruler but...well its not too accurate any way u go about it. and how do u find the centerline of the fingerboard? and how do u draw straight frets off of that centerline? what do u use to make these marks? tape, pencil, grease, charcoal? this is only about drawing out the plans, not about the actual slotting. it seems like this part may be the more difficult.