Polar planimeter for measuring areas on a sphere! (Amsler,
1884)
Measures average radius of a curve from a point
By Green's Theorem this equals a quantity proportional to the electric potential at a point due to a region of uniform electric charge.
Radial Square Root Planimeter
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What do these do?
Moment Integrator (Amsler, late 1800's)
Measures area, centroid, and moment of inertia
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