Many measuring instruments are fittd with a vernier, a subsidiary scale for making subdivisions of the main measuring scale. For subdividing a main scale in units of ten the vernier has ten equal divisions totalling the length of nine of the main scale, and the reading is taken from the vernier where alignment takes place on the divisions of both scales. Some vernier gauges are made which can be read to 0. 01 mm; a vernier protractor divides degrees of a circle into minutes.