A Mortise and Tenon Primer
(I have no affiliation with with Glen-Drake - just picked up the shorter version at a woodworking show a few years back and reach for it often. Will be ordering a pair of the mortise markers and the longer rod after the Christmas Crunch)
THIS IS A MUST HAVE tool if you're going to be doing almost any type of joinery other than biscuits or pocket hole screws. Ain't cheap but if you want to scribe a line with precision, with one vertical face where you want one, then the Tite-Mark is worth every penny.
With the recent additon of the Mortise accessory, this tool is as close to perfect a precision marking tool as you can get for a woodworker's tool cabinet.
Now let me show you how handy this thing is for laying out a mortise and corresponding tenon --->