'Setting circles' are angular measurement scales that can be placed on the two main rotation axis of some telescopes.

They may also be equipped with setting circles to allow for the location of objects by their celestial coordinates.

Historically setting circles have rivaled the telescopes optics as far as difficulty in construction.

Making a set of setting circles required a lot of precision crafting on a dividing engine.

In the 20th century setting circles were replaced with electronic encoders on most research telescopes.

Also, even the finest graduations on setting circles are usually more than a degree apart, which makes them difficult to read accurately, especially in the dark.

Equatorial mounts could then be accurately pointed at objects with known right ascension and declination by the use of setting circles.

It can be used in place of or in conjunction with setting circles.

This was a Thomas Cooke equatorial with setting circles and a driving clock.

"In the past, they've set 100-foot circles around eagles' nests."