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Total Indicator Reading

Total Indicator Reading (TIR) measures roundness in relationship to a center line. TIR is expressed in total diametric deviation: ±0.004 (0.102mm) deviation is defined as ±0.008 (0.203mm) TIR. Roundness tolerances for molded plastic parts should not exceed ±0.007 per inch diameter (0.07mm/cm), with a minimum TIR of ±0.005 (0.127mm).