Drum tuner.
https://diqn32j8nouaz.cloudfront.net...l_fullsize.jpg
In use, 4:37 video:
https://www.youtube.com/watch?v=oU7Tbw7K-vc
Previously:
https://www.homemadetools.net/forum/...223#post180707
https://www.homemadetools.net/forum/...865#post137272
https://www.homemadetools.net/forum/...911#post167827
https://www.homemadetools.net/forum/...809#post148312
https://www.homemadetools.net/forum/...590#post151610
