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Diameter (D_{a} and D_{b})

Measure the largest Diameter (D_{a}) Measure the smallest Diameter (D_{b})

Heigth (h)

Measure the height (h) vertically and not alongside the edge.

The math

The formula for a spherical frustum might seem difficult, and I guess coming up with the formula in the first place was. As it is, it's no harder to use than any other formula. Put the right numbers into the right slots, and you are there. The a is d_{a} divided in 2 to give the radius. The b is d_{b} divided in 2 to give the radius.

About

If you chop the top and bottom of a sphere you get a spherical frustum.