Description

A two-sided plotting scale in ivory of length 6 in (also known as a Georgian scale). It has a scale of chords and scales dividing the inch into 40, 35, 30, 25, 20, and 15 parts on Side A. The other side (Side B) has an inch scale divided to 1/10″ and numbered by ones from 1 to 6; a scale divided to ones and numbered by tens from 10 to 50 (10 units is approximately 3 cm); and 5″ plotting scales with diagonal scales at each end. One plotting scale is divided to 1/2″ and numbered by ones from 10 to 1, and the other is divided to 1/4″ and numbered by ones from 1 to 18. One edge of the rule is scalloped.

In practice, a plotting scale and a divider are used together. Firstly, the divider is used to span a distance on a plan. Secondly, the divider is moved to the plotting scale to read the distance based on the scale of the plan. The reverse process may also be used to plot a specific distance from the scale onto the plan.