Math compasses are technical drawing instruments that have been around since ancient times, as the Greeks used them for a myriad of purposes. These compasses are most commonly utilised in math (especially geometry) for making accurate circles and arcs and for constructing angles, which makes them an essential school supply. Even with the rise of graphing calculators and computer applications, math compasses remain popular because the hands-on nature of them makes it easier for most students to grasp the math principles behind the exercise.
When choosing a math compass, it's important to first consider the types of compasses, materials used to make them, the quality of various compasses, and certain specifications. This will ensure the right compass is purchased.
Math Compass Types
There are five main types of compasses. Though most have the same design philosophy, style differs. Most work just fine for common math applications, too. However, different people may like one type over another, so choose not only according to needs, but also according to preferences.
The most common kind of math compass, drawing compasses feature two arms connected on top by a hinge that can pivot. This makes widening or narrowing the drawing radius easier. The arm with the sharp point stabilises the compass, while the pencil arm (either a graphite-tip or pencil attached to a holder) draws.
In a beam compass, a straight edge ruler holds the two arms. The advantage is that these types of compasses have a larger drawing diameter and the ruler can be used to draw straight lines quickly.
Showcasing a scissor-like design, proportional compasses have two arms that cross each other. A hinge screw in the middle holds the arms together and allows them to widen and narrow with ease.
In a bow compass, a hinge screw connects two arms as well. An adjustable wheel is then used to position the two arms. Though these require a bit more work to manoeuvre, bow compasses are quite stable as most wheels can lock, which increases accuracy.
With a drop compass, the pencil arm can pivot, while the needlepoint arm remains in a fixed position. This benefits accuracy, but limits drawing diameter and how fast one can work.
Materials Used to Make a Math Compass
The material used to make math compasses plays a huge role in terms of quality and durability.
Metal (silver, brass, stainless steel, and aluminium) offer exceptional stability and durability, and usually make drawing accurate shapes simple. The only downside is the needle points may be too sharp for young users.
Wood is a durable and budget-friendly, but lacks the stability of metal compasses.
Plastic is a safe, inexpensive choice, but stability and accuracy typically fail to satisfy with such compasses.
Overall Quality of a Math Compass
Reviews tell a lot about the quality of a math compass. However, the best way to tell is to use one. Check to see that the compass can't be opened too easily, as one that swings open quickly probably has a weak hinge. Ideally, a little bit of pressure must be applied for the hinge to allow arm movement; this signifies a strong construction and that the compass will hold its place when drawing. If using a compass where the pencil is attached, make sure the pencil doesn't move or pop out when drawing; this is a common problem with many cheaply designed compasses; get a graphite-tip arm if possible.
Math Compass Specifications
It's also important to consider certain specifications when choosing a math compass. Length of compasses typically span between 3.9 - 7.9 inches (or exactly 10-20 centimetres); longer ones require more concentration to control properly, but offer a wider drawing range. Drawing diameter, which ranges from 5.9 inches to 14.1 inches, (or exactly 15-36 centimetres) or more, should also be factored; make sure to get one that can draw big enough circles. Weight can be anywhere from less than 1.4 to 2.1 ounces (or 40-60 grams); note lightweight compasses are easier to control, but be sure they're made of quality materials before getting one. If unsure about what specs are needed, buy a set that includes compasses that boast a variety of lengths, weights, and drawing diameters.
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