From before: AR - AL = l s - 1/2 l l2 Dq
With both polar and linear planimeters, the left end of the
planimeter follows a path that encloses no area: AL
= 0
AR = A, desired area
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In addition, the net rotation is zero: Dq = 0
A = l s
The area is proportional to the net roll of the
wheel,
and so can be read from a scale attached to the wheel.