vernier
Concise Oxford English Dictionary © 2008 Oxford University Press:
vernier /ˈvəːnɪə/
▶noun a small movable graduated scale for obtaining fractional parts of subdivisions on a fixed main scale of a barometer, sextant, or other measuring instrument.
– origin C18: named after the 16th-cent. French mathematician Pierre Vernier.
'vernier' also found in these Oxford entries:

