The number of revolutions a drill stem and bit must turn to advance the drill bit 1 in (2.54 cm) when the stem is attached to and rotated by a screw- or gear-feed-type drill swivel head with a particular pair of the set of gears engaged. (E.g., when a screw-feed swivel head of a diamond drill equipped with three pairs of gears, having a feed ratio of 100, 200, and 400, is operated with the 100-pair engaged, the drill stem must revolve 100 times to advance the bit 1 in, if the 200-pair is engaged, the drill stem rotates 200 times/in (508 times/cm) advanced, and if the 400-pair is engaged the stem must rotate 400 times to advance the bit 1 in).