Abstract: A positioner, such as a test head carrier for a semiconductor wafer and device tester, includes a vertical support and a main arm for supporting a test head. The main arm is suspended for vernier movement by use of a counterbalancing force such as counterweights. The suspension of the main arm is performed at a mechanical advantage so that reduced counter-blancing force and correspondingly large movements on the counterblance side are used to effect the vernier movement. The vertical support may be adjusted with a non-compliant drive such as a ball screw mechanism. The vernier movement can also be used to sense collisions and other positioning errors and actuation of the drive for the vertical support can be controlled accordingly.