Answer:

vernier

AnswerCrossword Clue
VERNIERScale for precise measurements
VERNIERFrench mathematician
VERNIERFrench inventor of slide scale (1580-1637).
VERNIERShort scale sliding on a longer one.
VERNIERSextant scale
VERNIERScale named for a French mathematician
VERNIERFine-detail scale