Recently there was a discussion about using a plunge router along with a home made jig to make a mortise.
Jig is simple enough; however, proper set up could be a little touchy since there are no centerlines, scales, etc to assist.
Tonight I'm scrounging thru a desk drawer and find some 8x8 grid paper used for graphic arts layouts.
BINGO.
Tape a piece of the 8x8 to the bottom plate with double back tape, then overcoat with a sheet of clear contact paper used to protect books, shelves, etc.
Now you have a reference grid to use for any set up that is protected which reduces accurate set up to a minimum.
Even a blind hog finds an acorn if he keeps rooting around long enough.
Lew