Is "Compasses" a typo?

In the Wikipedia article for Freemasonry, it gave a picture regarding the emblem of the Freemasons:

The caption below reads:

The Masonic Square and Compasses.
(Found with or without the letter G)

Just wondering, is "Compasses" correct? Shouldn't it be compass? I looked this up on several dictionaries, and I don't seem to find "compasses" when referring to a tool for drawing circles, only "compass". However, "compasses" makes sense, as it looks something similar to "scissors".

Should it be "compass" or "compasses"?

I think it is not a typo. I've looked up compasses in my Babylon English dictionary, and it says:

compasses
n. instrument for drawing circles and measuring, calipers.

Additionally, Oxford Dictionaries Online states there is also compasses or a pair of compasses.

compass
2) (also compasses or a pair of compasses) an instrument for drawing circles and arcs and measuring distances between points , consisting of two arms linked by a movable joint , one arm ending in a point and the other usually carrying a pencil or pen.

A compass, like scissors, tweezers, glasses, pliers, tongs, bellows, and calipers, is an instrument that is made up of two near-identical pieces that are attached to each other. Comparing it with these examples, it's somewhat surprising that we generally refer to it in the singular rather than in the plural. All three constructions: a compass, a pair of compasses, and compasses, are acceptable, although a compass is currently the general usage. As this Google Ngram shows, the plural compasses was formerly used much more often than it is now: