I have a tape measure, Don't know where I got it. .

It's maybe 10' long, a bit over 2" x 2", has a small level in the front
and a yellow scribing tool at the other end. Fine.

It also has a piece of clear lucite 2" x 2" on the side with the Home
Depot logo on it, and it's hinged at the top, but when the hinged part
is closed, it has an empty space about 2 mm. thick between the lucite
ann the black tape measure. What is this for?