Machinist's level. By Ca Lem. 13:59 video:
https://www.youtube.com/watch?v=7WFm4P29gNU
Previously:
https://www.homemadetools.net/forum/...368#post154515
https://www.homemadetools.net/forum/...766#post155997
https://www.homemadetools.net/forum/...989#post156973
