T Rule is used to read duct width, validate traverse hole locations and to mark traverse points (hole locations) on duct with pinpoint accuracy. It is not common to get a duplicate result of a duct traverse at the same location under the same condition. That is the nature of duct traverse, except the technician uses our auto duct traverse equipment. Irrespective, an accurate traverse begins with drilling the holes at the correct location. This is the only aspect of the traverse process that is visible and easily verifiable. If the holes are not located accurately, then what would be the integrity of the reading in the duct? The T Rule is indispensable for Engineers, TAB Supervisors, Commissioning Agents, Construction managers and administrators with oversight for the quality of the work.