First ray hypermobility has been linked to many abnormal conditions in the foot. First metatarsal vertical displacement is proportional to the measurement of first ray dorsiflexion. A new device that measures first ray mobility has been built and tested. The device applies a dorsiflexing force to the head of the first metatarsal and measures the amount of vertical displacement that results. The design and instrumentation of the device is described. A safe and reliable testing procedure for measuring maximal first ray displacement is discussed. Clinicians could use this measure when selecting treatment options for patients who suffer foot pathologies resulting from faulty mechanics of the first ray.