A measure used to gauge the roundness of a printing press roller, be it an ink or dampening roller used in offset lithography, an impression roller or gravure cylinder used in gravure, or an inking roller used in flexography. TIR is the difference in the lengths of a roller's radius as measured from the center to the outside surface. (A perfectly round roller would have a difference of 0 between different radii, as the radii of a circle are always equal regardless of where they are measured.) TIR is typically measured using a laser; the manufacturing tolerance of TIR is ±0.0005 inch, meaning that a roller can be out-of-round by that much before being deemed defective. An older roller that develops a TIR of greater than ±0.0005 inch should be replaced or repaired. Out-of-roundness of ink rollers is an important consideration; rollers that are elliptical (or eccentric) rotate with a bump that can cause streaking and other ink-transfer problems. An offset press roller's out-of-roundness can also be gauged using the stripe method of roller setting. (See also Impression Roller and Gravure Cylinder.)
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