Circumference

The ratio of the circumference of a circle to its diameter was represented by the Greek letter pi. (TV: The Five Doctors)

In 2007, a whiteboard in a classroom at Deffry Vale High School referenced the circumference of a circle. (TV: School Reunion)

Martian cruisers such as the Saavid sported three nacelles which protruded from the vessel at precisely 120 degrees around its circumference. (PROSE: The Jeopardy of Solar Proximity)

During the Revolution of the Ood, Klineman Halpen had detonation packs placed around the circumference surrounding the Ood Brain, intending to kill it. These explosives were deactivated by the Tenth Doctor. (TV: Planet of the Ood)