TIR stands for Total Indicator Reading, which is a term used in metrology and manufacturing to measure the difference between the maximum and minimum values measured across an entire rotating surface about a reference axis. TIR is also known as full indicator movement (FIM) and is used to measure roundness in relation to a center line. The symbol used for TIR is a connected double arrow along with a value referenced against a datum axis. TIR is important in manufacturing because it creates a boundary zone in which all points on the specified surface must fall between in order for the part to meet specifications.

It is important to note that TIR has other meanings in different contexts. For example, TIR can also refer to Traumatic Incident Reduction, which is a technique designed to examine the cognitive, emotional, perceptual, or other content of past incidents, to reduce or eliminate the emotional charge contained in them. Additionally, TIR can refer to Total Internal Reflection, which is the reflection of the total amount of incident light at the boundary between two media.