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To measure distances, rulers have printed length scales. They come in various sizes and shapes, often rectangular, with lengths 3 to 15 times their width. The example below shows a ruler with a length 7 times its width.
A ruler can be used as a straightedge to draw a segment between any two points. To do so, place the ruler's edge on both points and draw along it with a pen or pencil.
When using a ruler to measure distance between two points, align the ruler's edge with both points and start one point at 0. Then, read the distance directly from the scale.
Sometimes is not possible to start measuring from zero on the ruler. In such cases, align one of the points with any convenient mark or number on the ruler. Then, note the measurement where the second point aligns with the ruler. The distance between the two points is the difference between these two measurements.
