This week I would like to focus on an object that I have owned for a year and a half, but that I have only recently started using on a near daily basis. This object is my compass. It is not the type of compass that depicts what direction one is facing, but the kind of compass used to make perfect circles. I purchased this object for a class two fall semesters ago, yet we only needed to use it twice. However, this semester I am enrolled in a class by the name of Axiomatic Geometry, a class in which the compass is a vital tool.
My compass is metal, however they may be plastic as well. One side of the compass has a thick, needle-like structure on the end. The opposing side is created to hold a golf pencil (a small pencil, approximately four inches in length that does not have an eraser). The two sides are joined by a mechanism that allows them to smoothly glide in and out, changing the distance between them. The distance set will determine the size of the circles created. The compass has distance measurements in both inches and centimeters. The distance markings refer to the size of the circle’s diameter. The compass has no indication of what company created it, it merely says made in China and possesses no other identifying marks.
Despite the lack of identifying marks on the compass itself, I am able to track its origins from my Amazon order. According to my order history, this is a Charles Leonard Ball Bearing Compass. This brand has been around for over seventy years in the office supply industry. For this reason, on Amazon, the company writes a claim that they can guarantee quality and value. The compass is able to create circles with up to a twelve inch diameter. It has increased in price by $0.33 since I purchased it in August of 2017. The price I paid was $4.31, the compass now costs $4.64.
The first known compasses did not have a pencil or a pen on one end, but a needle on each end. It was invented by Galileo in the late 1500s in an attempt to create a universal mathematical tool for arithmetic and geometry. This compass would make circles and arcs by leaving scratch marks on the surface. Compasses can also measure length and move a length, despite the fact that the unit of measurement for the length will not be provided by the tool.
I have now learned how this tool works in the geometrical context. While it can technically only make circles and arcs, the circles and arcs can create so much more. For example, using only a line segment and a compass, one can create a perfect equilateral triangle. Other examples of what can be created on a mathematically perfect level include angle bisectors, replications of a given angle, replications of a given quadrilateral, a perpendicular line, etc. I was unaware as to how much could be done with this tool until I began taking a class that focuses on it. I find it fascinating how sometimes the simplest mechanisms can do so much.
Sources:
https://brunelleschi.imss.fi.it/esplora/compasso/dswmedia/storia/estoria1_st.html
http://www.historyofpencils.com/drawing-tools/drawing-compass/
The Materials of History, Thought, and Art 
Brooke,
I also use a compass frequently (I have one identical to yours, actually). I never knew that they were invented by Galileo though! I never seem to get a smooth pivot with metal compasses, but then again, perhaps it’s better for them to be a bit stiff for drawing. I also really appreciate that you picked it out of all things, and expanded it from a simple 2 bar mechanism out to an invaluable tool. Drawing a circle seems like something you can do with just a pencil, but without one of these it’s near impossible!