What tool measures the trueness of a shaft?

The tool that measures the trueness of a shaft is a dial indicator, often referred to as a dial meter. This precision instrument can detect small variations and deviations in the shaft's alignment and roundness, making it essential for ensuring that rotating machinery operates smoothly and efficiently.

Dial indicators work by using a probe that extends to contact the surface of the shaft. As the shaft rotates, any deviations from true alignment will cause the indicator needle to move, translating the small movements into measurable readings on the dial. This allows technicians to identify misalignments or imperfections in the shaft, which can be critical for the performance and longevity of machinery.

Other tools mentioned, such as calipers and tape measures, are used for measuring dimensions and lengths, but they don’t provide the specific readings that indicate how true a shaft is. A laser level, while useful for establishing horizontal or vertical planes, is not designed to gauge the accuracy of a shaft's rotation. Thus, the dial indicator is the most suitable tool for measuring the trueness of a shaft.