Note 1 — ESTIMATING.
Reading edition
A practical rule in finding the area of a circle is to multiply one-half the diameter (radius) by itself and the product by22/7. In finding the volume in the wall of a circular structure, such as a silo or tank, the area of the circle formed by the inside circumference is deducted from the area of the circle formed by the outside circumference and the remainder is multiplied by the height.