Modern disc brake systems often have extremely narrow tolerances requiring perfectly straight rotors for optimal performance and freedom from rubbing and noise. The DT-3i.2 bolts directly to the DT-3 Rotor Truing Gauge and magnifies even the smallest of rotor deviations, displaying them on an easy-to-read dial indicator capable of displaying measurements as small as 0.01 millimeter. The readout from the dial indicator allows the user to determine the straightness of the rotor in real numbers and work toward an acceptable range of variance. The fully adjustable elongated tip helps the DT-3i.2 to accommodate most bicycle disc brake rotors, including irregularly-shaped rotors.