What is the purpose of the ratchet stop on an outside micrometer?

The ratchet stop on an outside micrometer serves a critical function in ensuring the accuracy of measurements by allowing the user to apply consistent pressure when taking a reading. When measuring an object, it is essential to ensure that the micrometer’s anvil and spindle make proper contact with the workpiece without over-compressing it. The ratchet stop provides an audible click that indicates the correct amount of pressure has been applied, thus preventing slippage and ensuring that the measurement remains stable.

Having this feature helps to maintain precision when measuring multiple objects or during repeated measurements, as it reduces user error related to the application of excessive or insufficient pressure. The ratchet mechanism also allows for a tactile feedback that reassures the user of consistent measurement practices.

The other choices describe functions that are not related to the primary purpose of the ratchet stop. Temperature measurement, instrument calibration, and adjustment of the measurement scale each pertain to different aspects of measurement or instrument function, which do not directly involve the operation of the ratchet mechanism.