Planimeter.
Fullsize image: https://s3-us-west-1.amazonaws.com/h...r_fullsize.jpg
https://s3-us-west-1.amazonaws.com/h...planimeter.jpg
More: https://en.wikipedia.org/wiki/Planimeter
Previously:
https://www.homemadetools.net/forum/...631#post147559
https://www.homemadetools.net/forum/...857#post163940
https://www.homemadetools.net/forum/...743#post159676
https://www.homemadetools.net/forum/...820#post148359
https://www.homemadetools.net/forum/...422#post142646
https://www.homemadetools.net/forum/...041#post140930
https://www.homemadetools.net/forum/...032#post137890