A vernier scale is often included, which allows the position to be read to a fraction of the smallest scale mark. Source: Internet
The angle of the sight is then read from the scale on the arc, making use of the micrometer or vernier scale provided. Source: Internet
Vernier Micrometer sleeve (with vernier) reading 5.783mm Some micrometers are provided with a vernier scale on the sleeve in addition to the regular graduations. Source: Internet