Determining an angle is one of the more common applications for measuring tools. Starrett offers a wide variety of products to perform this task to various degrees of accuracy, as appropriate for different applications. The focus of this article is on two very different tools, each of which can provide ultra-precise angle measurement.

Starrett-Webber Angle Blocks
Angle gage blocks provide fast, very simple and extremely accurate measurements of any angle.

One traditional method of angle measurement from a surface involves a sine bar and gage blocks. Determining the angle with this method requires working with trigonometric formulas and complicated stacks of rectangular gage blocks.

Angle blocks are far simpler to use. A set of Starrett-Webber angle gage blocks consisting of only 16 blocks will measure 356,400 angles in steps of one second, to an accuracy of 1/5,000,000th of a circle. Either plus or minus positions of any angle can be measured quickly and easily with only a few of these micro-accurate blocks.

For example, to obtain a measurement of 35°, use the 30° angle and add the 5° angle (making sure that both plus ends are together). To get a measurement of 25°, use the same two blocks, but bring them together so that the minus end of the 5° block is over the plus end of the 30° block, subtracting 5° from  30°, for a 25° measurement.

Starrett-Webber angle gage blocks are available in three accuracies: ±1 second Reference Grade, ±2 second Calibration Grade, and ±5 second Working Wrade.

Precision Universal Bevel Vernier Protractor
The Universal Bevel Vernier Protractor can measure any angle to 1/12th of a degree or 5 minutes.

The blade and dial can be rotated as a unit to the desired position and locked in place with the dial clamp nut. The ultra sensitive adjustment permits very accurate settings. The blade can be extended in either direction and locked against the dial by tightening the blade clamp nut which operates independently from the dial clamp nut.

The protractor dial is graduated 360°, reading 0-90°, 90°-0, 0-90°, 90°-0. Each ten degrees is numbered, and each five degrees is indicated by a line longer than those on either side of it. The Vernier plate is graduated so that 12 spaces on the plate occupy the same space as 23 spaces on the disc of the protractor.

The difference between the width of one of the 12 spaces on the Vernier and two of the 23 spaces on the disc of the protractor is therefore 1/12 of a degree, or 5 minutes (5'). Each space on the Vernier is 1/12 of a degree, or 5 minutes (5') shorter than 2 spaces on the disc.

The Vernier plate has clear figures each third space. These figures represent minutes. When the 0 line of the Vernier plate coincides exactly with a graduated line on the disc of the protractor, the reading is exact in whole degrees.

When the 0 line of the Vernier plate does not coincide exactly with a graduated line of the disc of the protractor, find the line on the Vernier that exactly coincides with a line on the disc of the protractor. This line on the Vernier indicates the number of twelfths of a degree or 5 minutes (5') that should be added to the reading in whole degrees.