TIR (total indicator runout) is the full range shown by a dial or electronic indicator as its contact follows a rotating or moving surface in a defined setup. The result is the difference between the highest and lowest observed readings.
TIR is setup-dependent. The indicated range can reflect the spindle, taper, holder, test bar, workpiece, jaw condition, dirt, contact location or the measurement setup itself. It is useful evidence, but one reading does not identify the cause or prove the complete accuracy of a machine.
In shop conversation, TIR commonly means the observed total indicator range. On an engineering drawing, circular runout and total runout are geometric controls tied to a datum reference framework. Do not substitute an undocumented shop reading for a drawing requirement or an acceptance test.
Ask where the reading was taken, which tool or test bar was used, how far the contact was from the reference face, whether the spindle was warm, the instrument resolution, the machine state and whether the result repeated. Use the machine builder's procedure and a qualified inspector when the result affects safety, acceptance or value.
ASME — Y14.5 Geometric Dimensioning and Tolerancing identifies the governing GD&T framework that includes runout controls. See the Machine Blue Book methodology for evidence and inspection boundaries.
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