Scales of measurement. Every ruler has two sides, each depicting a scale of measurement. On one side, you will find the metric system for marking length and on the other side is the English scale. The metric scale measures length or distance in millimeters and centimeters whereas the English scale uses inches and feet.
Using the metric scale. A standard ruler is usually about a foot long, or in metric terms, about 30 centimeters. You will find the ruler marked with lines which are designated with numbers from 1 to 30 and between each set of numbers, there are smaller lines which indicate the number of millimeters. Ten millimeters or mm equal 1 centimeter or cm, hundred cm equals one meter and so on. To measure the length between two points on a paper or other medium, place the ruler with the first centimeter line (which can be tagged as zero) on the first point. Mark the number at which the second dot on the paper corresponds to the centimeter reading, on the ruler. For example, with one point placed against the zero mark and the second point shows a reading of 3. In this case, the distance in centimeters between the two points is 3cm. If the point is actually placed at a point beyond 3 but well within the line depicting 4, count the smaller lines which show the millimeter scale and count the number of lines at which the point rests, say at the 5th small line, in which case the distance between the two points is 3.5cm or 35mm.
Using the English scale. The other side of the ruler measures length in feet and inches and this is the scale of measurement used in the US. One foot equals 12 inches and between each inch on the ruler are smaller markings in sets of eight. These are referred to as eighths of an inch. Following the same instructions as in step two, you can find out the distance in inches and eighths of inches. Using the same two points in the example above, the length will read as 1 and 2/8 or one and two-eighths of an inch.
Important tips. While using a ruler make sure that you place and hold it firmly against paper or other medium, say, like a wall. Keep it in a straight line always, whether placing it horizontally or vertically. To validate your measurements, you can always take down readings in both centimeters and inches and divide the metric measurement by 2.54. If the reading you've taken is accurate the quotient of this division will equal the number of inches you've measured.


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