Technical Performance Indicators of Measuring Tools
Nominal Value of the Measuring Tool
The value marked on the measuring tool to indicate its characteristics or to guide its use. For example, the dimensions marked on gauge blocks, the dimensions marked on ruled scales, and the angles marked on angle gauge blocks, etc.
Graduation Value
The difference in value represented by two adjacent graduations (the smallest unit of value) on the scale of a measuring tool. For instance, if the difference in value represented by two adjacent graduations on the micrometer drum of an external micrometer is 0.01mm, then the graduation value of that measuring tool is 0.01mm. The graduation value is the smallest unit of value that a measuring tool can directly read out, reflecting the level of reading precision and indicating the level of measuring accuracy of the tool.
Measuring Range
The range from the lower limit to the upper limit of the measured value that a measuring tool can measure within the allowed uncertainty. For example, the measuring ranges of external micrometers include 0～25mm, 25～50mm, etc., and the measuring range of a mechanical comparator is 0～180mm.
Measuring Force
The contact pressure between the measuring tool's measuring head and the measured surface during the contact measurement process. Too much measuring force can cause elastic deformation, while too little can affect the stability of contact.
Indication Error
The difference between the indicated value of the measuring instrument and the true value of the measured quantity. Indication error is a comprehensive reflection of various errors inherent in the measuring instrument itself. Therefore, the indication error varies at different working points within the instrument's indicated value range. Generally, gauge blocks or other metrological standards of appropriate precision can be used to verify the indication error of measuring tools.
