A K+E Radial Planimeter, from 1920s. It measures the average radius of a roughly circular shape!
This is episode 76 of my video series about old calculating devices.
Radial planimeter instructions: https://archive.org/details/radialinstructions
End song inspired by "Hotter than a Molotov" by The Coup.
Chris Staecker webarea: https://faculty.fairfield.edu/cstaecker
#planimetria