Drill guage for 7x12 Lathe

Update: There is a new thing which uses a digital caliper. It's more compact, more stable and easier to read.
http://www.thingiverse.com/thing:17970
This is about as simple a thing as I can imagine. But it serves a purpose for those with a 7 x 12 lathe so here it is.
I have seen several examples of this solution for determining drilling depth with a lathe. In each case the operator used aluminum or acrylic or some other material which required machining. I was thinking along the same lines, d