Direct measurement: directly measure the measured parameter to obtain the measured size. For example, measure with calipers and comparators.
Indirect measurement: measure the geometric parameters related to the measured size, and obtain the measured size through calculation.
Absolute measurement: The reading value directly indicates the size of the measured size, such as measuring with a vernier caliper.
Relative measurement: The reading value only represents the deviation of the measured size relative to the standard quantity. If a comparator is used to measure the diameter of the shaft, it is necessary to adjust the zero position of the instrument with a measuring block first, and then measure. The measured value is the difference between the diameter of the side shaft and the size of the measuring block, which is relative measurement. Generally speaking, the relative measurement accuracy is higher, but the measurement is more troublesome.
Contact measurement: The measuring head is in contact with the surface to be contacted, and there is a mechanical measuring force. Such as measuring parts with a micrometer.
Single measurement: measure each parameter of the tested part separately.
Comprehensive measurement: Measure the comprehensive index reflecting the relevant parameters of the part. For example, when measuring the thread with a tool microscope, the actual pitch diameter of the thread, the half-angle error of the tooth profile and the cumulative error of the pitch can be measured separately.