The aim of this study was to evaluate the intrasession-, intersession-, and interrater reliability of a vernier caliper measurement of mandible movements. The authors calculated the intrasession, intersession-, and interrater reliability using a plastic caliper for important mandibular parameters. All intraclass-correlation-coefficients (ICC) are at least moderately accurate, especially the values for intrasession- and intersession reliability, which were excellent. Only the interrater reliability shows greater fluctuations. Whereas the mouth opening, protrusion, and the tooth positions are reliably correct, the same was not applicable to the side movements. The lateral movement measurements were highly variable. This did not apply to other movements. Patient compliance is important along with a different mouth-opening angle. It is possible to generate a variable laterotrusion to both sides. The caliper investigated is a fast, simple, and inexpensive tool for daily work.