Make: Volume 77

perform a different job, and each was given a

special name. By far, the most important scale

was the one that Galileo called the Line of Lines.

The Line of Lines is the one you need to multiply,

divide, and find proportions.

Another important scale is called the Line of

Circles. With it, you can measure the radius or

diameter of any circle and quickly determine

its circumference. (It also works in the other

direction, allowing you to find the diameter of a

circle for a given circumference.)

As Figure

D

shows, the sectors made by

London instrument makers in the 18th century

were chock full of scales or “lines.” Many of

them were rather specific ...