Metrology Loop - The path that weaves through the assembly chain from one machine element to another which provides a machine's positioning reference. Although the metrology loop does not provide physical support as the structural loop does, it's path may interlace through those supporting components and be affected by their thermal expansion, force distortions, and misalignments. See also, metrology frame, dynamic loop, frame.

• For a machine tool, the metrology loop between the workpiece and tool may interlace through such components as the spindle, quill, table, carriages, scales, ballsrews, frame and workpiece clamping fixture.