What does this sentry theorem say, and why has it been given this name?

Question

I know the sentry theorem says that "The sum of the exterior angles of any polygon — one at each vertex — is 360 degrees."

Can someone help me to understand why it has been given this name?

Answer 1

After reading your question, I wanted to know the answer too!

A sentry is a soldier or guard who walks around the perimeter of a camp or stronghold.

The sentry theorem can be explained by the fact that if you were to walk around a polygon, you would complete a full revolution (360°). The only place I could find a reference to this meaning was on a twitter feed by Carmel Schettino (https://twitter.com/schettinopbl/status/555736502471524354), but it makes sense to me!