AS B139-1955

Relates to three mechanical types of bevel protractors, in which the measurement is read direct from the scale either with or without the assistance of a vernier, and for one optical type in which the measurement is read on an internal circular scale by means of an optical magnifying system integral with the instrument. Requirements for accuracy in respect of the body, stock and blade, and of the accurate angle attachment, where fitted, are given and graduations for both types of protractors are specified. Illustrations of the nomenclature adopted and clauses relating to material, workmanship, and marking are included.