The indication of the measuring instrument directly reflects the measurement of the measured value as measurement. Measuring the diameter of a shaft with a vernier caliper and an outside micrometer is not only a measurement, but also a measurement. The cartoning production line compares the measured value with a standard value to obtain the measurement of the difference between the two as a relative measurement. If the inner diameter dial gauge is used to measure the pore size, it is a relative measurement. Contact measurement and non-contact measurement: the measurement of the presence of the measuring force that the probe of the measuring instrument is in contact with the surface of the measured object is the contact measurement. Such as measuring the surface roughness with a light-cutting microscope is a non-contact measurement. Single measurement and comprehensive measurement: The measurement of a single parameter that is not related to each other is called single measurement. Simultaneous measurement of multiple parameters and the measurement of their combined effects. Measuring the middle diameter, half angle and pitch of the thread with a measuring instrument separately is a single measurement; while detecting the thread with the through end of the thread gauge is a comprehensive measurement. Passive measurement and active measurement: the measurement after the product is processed is passive measurement; the measurement in the process of processing is active measurement. Passive measurement can only find and pick out unqualified products. The active measurement can control the processing of the equipment through the feedback of the measured value, and the generation of non-conforming products.