How to Construct a 15 Degree Interval on a Line

The Earth

A degree (°) is a measurement of plane angle. One degree represents 1/360th of a rotation, or 1/30th of a full circle. A 15-degree interval is used for time zones: the Earth is divided into 24 time zones, each with a 15-degree interval. At first glance, it might seem difficult, or even impossible, to divide a line (measured in inches or centimeters) into 15-degree segments (measured in angles). The trick is to realize that angular measurements are relative to the object you are working with.

Instructions

1. Ask yourself the question: "What does the line represent?" Most often, a line that you would be asked to draw 15-degree intervals on is the equator, which wraps around the Earth at the center.

2. Measure your line with a ruler.

3. Divide the line into 24 equal segments (because 24 * 15 degrees = 360 degrees) if your line represents the equator. For example, if your line (in Step 2) was 12 inches, then:
   12 inches / 24 = 0.5 inches

4. Draw vertical lines at each interval using the right angled set square. Start at zero. For the 12-inch line used as an example, you would draw vertical lines at the 0-inch mark, the 0.5-inch mark, and every 0.5 inches until the 12-inch mark, where you would draw the final vertical line.

Tips & Warnings

• If your line represents 1/2 of the equator, divide your line into 12 segments (because 12 * 15 degrees = 180 degrees).

References

• Montana State University: Mapping