Concrete crack gauge.
Fullsize image: https://s3-us-west-1.amazonaws.com/h...e_fullsize.jpg
https://s3-us-west-1.amazonaws.com/h...rack_gauge.jpg
Previously:
https://www.homemadetools.net/forum/...272#post181015
https://www.homemadetools.net/forum/...907#post183667
https://www.homemadetools.net/forum/...536#post155083
https://www.homemadetools.net/forum/...254#post138591
https://www.homemadetools.net/forum/...829#post171214