Rulers, Straightedges, Compasses and Dividers
The handy group of measurement tools
We all learned how to use a ruler in elementary school, if not before. Little did we know at that age how many varieties existed and how many important purposes were to be served by the rulers of the world. For home use, several different sizes and configurations are available and useful, depending upon the work you do.
The Bench Rule. As its name suggests, you keep this one on your bench. Typically, it’s 12 inches long, with one edge marked off in sixteenths, the other in millimeters. The bench rule is handy for simple measurements, for adjusting your compass or dividers, and a miscellany of measuring tasks.
The Yardstick. Though not essential, the yardstick can be a handy tool to have hanging on the wall near at hand.
The Machine Rule. This six-inch-long rule is especially useful on the job site for reading drawings.
Straightedge. This heavy steel rule comes in a number of sizes (typically from one to six feet in length). One side is beveled.
Despite the absence of dimensions on its edge, a straightedge is invaluable for a number of tasks. You can use the beveled edge as a cutting guide. And when you hold the rule on its edge, it will instantly reveal whether a board or other surface is flat, convex, or concave.
Whether you’re drawing a circle or getting ready to cut an arc onto a sheet of plywood, you’ll need a compass. This age-old tool can perform a range of other duties as well.
The Compass. The compass enables you to draw circles or arcs. One of the legs ends in a point that is fixed at the center of a circle, while the other has a pencil or pencil point at its tip. Depending upon the nature of your work, you may require a simple drafting compass (for circles up to about 10 inches) or a larger model.
The Dividers. Dividers are used to step off measurements, or to transfer dimensions from a drawing to a workpiece or from a model to a piece in work. These tools closely resemble the compass, differing only in that both legs end in sharp points.
A variety of purpose-made dividers can be purchased. There is also a whole family of related tools, among them calipers, inside and out, micrometers and slide calipers, and others, some of which are accurate to .001 inch. For most people, though, a single combination compass-divider will fulfill likely needs.