In woodworking, one of the first things you learn how to do is "true" wood. It's an essential step; the necessary preparation for assured work. Each face and edge must be made perpendicular to the other. (I was going to describe the process here. However, it's one of those things that's fairly easy to do - once you've learned - but hard to describe, so I'll spare you, and myself, the details.) Trueness is more important than the numerical accuracy of measurement. If, for instance, you must make two sides of a cabinet, each of which is supposed to be 3/4" thick, 16" wide and 30" tall, it's much more important that the two sides be absolutely "true" (and identically mirror each other) than it is for both pieces to be absolutely 30" long. Or exactly 16" wide. Or 3/4" thick.
the coast of Britain? So much for rulers. Next week I'll be giving a little presentation about my workshop at a meeting of the Central Jersey Woodworkers Association. I'm a member there - very pleasant people, very enjoyable events. Originally, the presentation was to be about planes, but, honestly, that subject could use a rest. So I'll be "Shop of the Month" and use that as a way of talking about...other things. But what?