(1) The characteristic of measuring the thickness and height of the chord teeth in the indexing circle is that when measuring the thickness of the chord teeth in the indexing circle, the tooth tip circle should be used as the measurement reference. However, the accuracy requirements for the tooth tip circle are not high in actual gear operation, so the design and processing accuracy of the tooth tip circle are generally low, which affects the measurement accuracy of the chord tooth thickness.

(2) The characteristic of measuring the thickness and height of fixed chord teeth is that when calculating the measurement value, it is only related to the modulus and tooth shape angle of the tested gear, and is independent of its tooth number. In addition, the modulus and tooth shape angle of the standard gear have been standardized, making calculation very convenient. But when measuring the thickness of fixed chord teeth, the tooth tip circle should also be used as the measurement reference, which affects its measurement accuracy.

(3) The characteristic of measuring the length of the common normal is that the measuring tool is simple, the measurement is convenient and accurate, and the manufacturing error of the tooth top circle has no impact on the measured value of the common normal length.

The latter two measurement methods are used in actual production.