![]() It is the compass in the most simple form. Some compasses can be used to draw circles, bisect angles and, in this case, to trace a line. Scribe-compasses is an instrument used by carpenters and other tradesmen. Euclid showed in his second proposition (Book I of the Elements) that such a collapsing compass could be used to transfer a distance, proving that a collapsing compass could do anything a real compass can do.Ī beam compass is an instrument, with a wooden or brass beam and sliding sockets, cursors or trammels, for drawing and dividing circles larger than those made by a regular pair of compasses. The most rigorous definition of this abstract tool is the "collapsing compass" having drawn a circle from a given point with a given radius, it disappears it cannot simply be moved to another point and used to draw another circle of equal radius (unlike a real pair of compasses). Although a real pair of compasses is used to draft visible illustrations, the ideal compass used in proofs is an abstract creator of perfect circles. The hinge is set in such a way that the distance between the spikes on the map represents a certain distance in reality, and by measuring how many times the compasses fit between two points on the map the distance between those points can be calculated.Ĭompasses-and-straightedge constructions are used to illustrate principles of plane geometry. The radius of the intended circle can be changed by adjusting the initial angle between the two legs.ĭistances can be measured on a map using compasses with two spikes, also called a dividing compass (or just "dividers"). Some people who find this action difficult often hold the compasses still and move the paper round instead. This holds the pencil lead or pen in place.Ĭircles can be made by pushing one leg of the compasses into the paper with the spike, putting the pencil on the paper, and moving the pencil around while keeping the legs at the same angle. The better quality compass, made of metal, has its piece of pencil lead specially sharpened to a "chisel edge" shape, rather than to a point. Alternatively, an ink nib or attachment with a technical pen may be used. The pencil lead draws the circle on a particular paper or material. The needle point is located on the steady leg, and serves as the center point of the circle that is about to be drawn. This sort of compass is often known as a "pair of Spring-Bow Compasses". The better quality compass, made of plated metal, is able to be finely adjusted via a small, serrated wheel usually set between the legs (see the "using a compass" animation shown above) and it has a (dangerously powerful) spring encompassing the hinge. The hinge can be adjusted, depending on desired stiffness the tighter the hinge-screw, the more accurate the compass’s performance. The screw through the hinge holds the two legs in position. ![]() Each has a separate purpose the steady leg serves as the basis or support for the needle point, while the adjustable leg can be altered in order to draw different sizes of circles. There are two types of leg in a pair of compasses: the straight or the steady leg and the adjustable one. Users can grip it between their pointer finger and thumb. The handle, a small knurled rod above the hinge, is usually about half an inch long. Typically one leg has a spike at its end for anchoring, and the other leg holds a drawing tool, such as a pencil, a short length of just pencil lead or sometimes a pen. Today those facilities are more often provided by computer-aided design programs, so the physical tools serve mainly a didactic purpose in teaching geometry, technical drawing, etc.Ĭompasses are usually made of metal or plastic, and consist of two "legs" connected by a hinge which can be adjusted to allow changing of the radius of the circle drawn. By the mid-twentieth century, circle templates supplemented the use of compasses. Prior to computerization, compasses and other tools for manual drafting were often packaged as a set with interchangeable parts. Compasses can be used for mathematics, drafting, navigation and other purposes. As dividers, it can also be used as a tool to mark out distances, in particular, on maps. A beam compass and a regular compass Using a compass A compass with an extension accessory for larger circles A bow compass capable of drawing the smallest possible circlesĪ compass, more accurately known as a pair of compasses, is a technical drawing instrument that can be used for inscribing circles or arcs. For other uses, see Compass (disambiguation). ![]() This article is about the drafting instrument.
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