[ThomasPowers]

Yes it's a hook rule; but by leaving a bit more of the tongue on it's also a square (and a 45 or other degree if you go that route).

Now it's not a shrink rule and my hats off to you if you make one that is! I found a 4 scale shrink rule at the fleamarket once for US$3 and snatched it up but gave it to a friend who did metal casting.

You notice how putting a measuring tape on hot steel causes problems? This simple to makle took deals with getting accurate measurements on hot steel. My rule has inside and outside scales too. Using calipers could be a way around the hot stuff as well.