The ratchet speeder increases the speed at which the spindle rotates, so the space between the anvil and the spindle is reduced more quickly than it would be if the thimble were used.
Using the ratchet speeder reduces the time it takes to use the micrometer.
The ratchet incorporates a slipping clutch mechanism that prevents over-tightening and aids the user to apply a constant measuring force to the spindle, helping to ensure reliable measurements.