The bevel protractor is used to establish and test angles to very close tolerances. It reads to 5 minutes or 1/12° and can measure any angle from 0° to 360°. The bevel protractor consists of a beam, a graduated dial and a blade which is connected to a swivel plate (with Vernier scale) by thumb nut and clamp. When the edges of the beam and blade are parallel, a small mark on the swivel plate coincides with the zero line on the graduated dial. To measure an angle between the beam and the blade of 90° or less, the reading may be obtained direct from the graduation number on the dial indicated by the mark on the swivel plate. To measure an angle of over 90°, subtract the number of degrees as indicated on the dial from 180°, as the dial is graduated from opposite zero marks to 90° each way.
Since the spaces, both on the main scale and the Vernier scale, are numbered both to the right and to the left from zero, any angle can be measured. The readings can be taken either to the right or to the left, according to the direction in which the zero on the main scale is moved.
Reading the Vernier scale:
The bevel protractor Vernier scale may have graduations of 5′ (minutes) or 1/12°. Each space on the Vernier scale is 5′ less than two spaces on the main scale. Twenty four spaces on the Vernier scale equal in extreme length twenty three double degrees. Thus the difference between the space occupied by 2° on a main scale and the space of the Vernier scale is equal to one twenty-fourth of 2°, or 5′.
Read off directly from the main scale the number of whole degrees between 0 on this scale and the 0 of the Vernier scale. Then count, in the same direction, the number of spaces from the zero on the Vernier scale to a line that coincides with a line on the main scale; multiply this number by 5 and the product will be the number of minutes to be added to the whole number of degrees.
For example: Zero on the vernier scale has moved 28 whole degrees to the right of the 0 on the main scale and the 3rd line on the vernier scale coincides with a line upon the main scale as indicated. Multiplying 3 by 5, the product, 15, is the number of minutes to be added to the whole number of degrees, thus indicating a setting of 28 degrees and 15 minutes.
A protractor is a geometry tool that measures the angle between two intersecting lines. For example, a protractor can measure the interior angle of a triangle, or a hexagon. One limitation of a regular, semicircle protractor is that it can only measure through 180 degrees. The bevel protractor solves this problem by having a movable arm that can extend to measure through 360 degrees. In addition, the bevel protractor is more accurate than a regular protractor: it can measure within 5 minutes (a minute is 1/60th of a degree).
Use
1. Unscrew the large clamp on the front of the protractor. This loosens the blade, so that you can swivel it.
2. Align the base of the protractor on one side of the angle, and them swivel the blade to form the other side of the angle. Tighten the large clamp.
3. Find the zero on the vernier scale. The vernier scale is the smaller scale on the inside of the protractor.
4. Read the number of degrees on the main scale, directly above the zero on the vernier scale. Say, for example, the zero on the vernier scale lines up with the 85 degree mark.
5. Read the minutes on the vernier scale. The minutes are found by looking counterclockwise on the vernier scale, and noting the first place where the line on the vernier scale lines up (exactly) with the line on the main scale. For example, the first line to match up with a line on the main scale is 30. This is measured in minutes, so the measurement is 30 minutes.
6. Add the degrees from Step 4 to the minutes from Step 5. In this example, the answer would be 85 degrees, 30 minutes.
Since the spaces, both on the main scale and the Vernier scale, are numbered both to the right and to the left from zero, any angle can be measured. The readings can be taken either to the right or to the left, according to the direction in which the zero on the main scale is moved.
Reading the Vernier scale:
The bevel protractor Vernier scale may have graduations of 5′ (minutes) or 1/12°. Each space on the Vernier scale is 5′ less than two spaces on the main scale. Twenty four spaces on the Vernier scale equal in extreme length twenty three double degrees. Thus the difference between the space occupied by 2° on a main scale and the space of the Vernier scale is equal to one twenty-fourth of 2°, or 5′.
Read off directly from the main scale the number of whole degrees between 0 on this scale and the 0 of the Vernier scale. Then count, in the same direction, the number of spaces from the zero on the Vernier scale to a line that coincides with a line on the main scale; multiply this number by 5 and the product will be the number of minutes to be added to the whole number of degrees.
For example: Zero on the vernier scale has moved 28 whole degrees to the right of the 0 on the main scale and the 3rd line on the vernier scale coincides with a line upon the main scale as indicated. Multiplying 3 by 5, the product, 15, is the number of minutes to be added to the whole number of degrees, thus indicating a setting of 28 degrees and 15 minutes.
A protractor is a geometry tool that measures the angle between two intersecting lines. For example, a protractor can measure the interior angle of a triangle, or a hexagon. One limitation of a regular, semicircle protractor is that it can only measure through 180 degrees. The bevel protractor solves this problem by having a movable arm that can extend to measure through 360 degrees. In addition, the bevel protractor is more accurate than a regular protractor: it can measure within 5 minutes (a minute is 1/60th of a degree).
Use
1. Unscrew the large clamp on the front of the protractor. This loosens the blade, so that you can swivel it.
2. Align the base of the protractor on one side of the angle, and them swivel the blade to form the other side of the angle. Tighten the large clamp.
3. Find the zero on the vernier scale. The vernier scale is the smaller scale on the inside of the protractor.
4. Read the number of degrees on the main scale, directly above the zero on the vernier scale. Say, for example, the zero on the vernier scale lines up with the 85 degree mark.
5. Read the minutes on the vernier scale. The minutes are found by looking counterclockwise on the vernier scale, and noting the first place where the line on the vernier scale lines up (exactly) with the line on the main scale. For example, the first line to match up with a line on the main scale is 30. This is measured in minutes, so the measurement is 30 minutes.
6. Add the degrees from Step 4 to the minutes from Step 5. In this example, the answer would be 85 degrees, 30 minutes.