vernier

noun

1. 1

   A secondary scale with finer graduations than the primary scale of a measuring device; the vernier measures between graduations of the larger scale.

2. 2

   A secondary control input with finer control than the primary, or coarse, input; for example the vernier frequency tuning knob on a radio.

3. 3

   A secondary system of force application for the attitude control of a spacecraft; for example a vernier thruster.