Diameters

Draw two concentric circles of differing diameters.

A caliper is an instrument for measuring thickness and internal or external diameters inaccessible to a scale or a ruler.

The yellow-poplar reaches heights of 80 to 120 feet (maximum recorded 198 feet) and diameters of 2 to 6 feet, with its straight, deeply furrowed trunk clear of limbs for much of its length.