Which tool is employed to measure alignment of a rotor shaft or the rotational plane of a disk?

The tool used to measure the alignment of a rotor shaft or the rotational plane of a disk is the dial indicator. This precision instrument is designed to measure small distances and deviations with high accuracy. It works by converting linear movement into rotational movement, allowing the user to detect misalignments in a shaft or disk by measuring runout or lateral movement.

When aligning rotors or disks, it is crucial to ensure they are perfectly level and aligned to prevent excessive wear and vibration during operation. The dial indicator can detect minute misalignments, which is essential for proper installation and functionality.

In contrast, a level is primarily used for checking horizontal or vertical alignment, while a caliper is used to measure dimensions such as length or thickness. A torque wrench is designed to apply a specific torque to a fastener and does not provide any measurement pertaining to alignment or rotational planes. Thus, the dial indicator is the appropriate tool for ensuring precision in alignment tasks in various mechanical and engineering applications.