Total Indicator Reading
Total Indicator Reading (TIR) measures roundness in relationship to a center line. TIR is expressed in total diametric deviation. Example: ±0.004 (0.10mm) deviation is defined as 0.008 (0.20mm) TIR.
TIR is the total lateral distance traveled by the indicator needle resting against the O.D. of a round part as the part is turned one full revolution.