1650s, rochet, from French rochet "bobbin, spindle," from Italian rocchetto "spool, ratchet," diminutive of rocca "distaff," possibly from a Germanic source (cf. Old High German rocko "distaff," Old Norse rokkr), from Proto-Germanic *rukka-, from PIE root *ruk- "fabric, spun yarn." Cf. rocket (n.2). Current spelling in English dates from 1721, influenced by synonymous ratch, which perhaps is borrowed from German Rätsche "ratchet."
1852, from ratchet (n.). Transferred sense attested by 1977. Related: Ratcheted; ratcheting.
To change by increments in one direction: Gold had ratcheted down to 385
[1977+; fr the ratchet action of a winch or of a wrench, where an increasing pressure, torque, pull, etc, is registered by the clicking of a pawl on a gear wheel]