BS 1685:2008

Explains the following types of bevel protractors: a) Mechanical - (i) Type A - With vernier graduated to read to five minutes of arc, and with slow motion device, and acute angle attachment. (ii) Type B - With vernier graduated to read to five minutes of arc, but without slow motion device or acute angle attachment. (iii) Type C - With scale graduated in degrees, without vernier or slow motion device or acute angle attachment. b) Optical - With an internal circular scale which is graduated in divisions of 10 minutes of arc and read against a fixed index line or vernier by means of an optical magnifying system integral with the instrument, enabling readings to be taken, by estimation or otherwise, to approximately two minutes of arc.

This standard relates to the following types of bevel protractors: Mechanical. Type A. With vernier graduated to read to five minutes of arc, and with slow motion device, and acute angle attachment. Type B. With vernier graduated to read to five minutes of arc, but without slow motion device or acute angle attachment. Type C. With scale graduated in degrees, without vernier or slow motion device or acute angle attachment. Optical. With an internal circular scale which is graduated in divisions of 10 minutes of arc1) and read against a fixed index line or vernier by means of an optical magnifying system integral with the instrument, enabling readings to be taken, by estimation or otherwise, to approximately two minutes of arc.