The RESR rotary encoders from Renishaw Inc. offer high-resolution, high-accuracy angular positioning. The low-mass, low-inertia design provides accuracy to ±0.5 arc sec, up to 129.6 million counts per revolution and speeds of >2900 rpm with no backlash. The noncontact optical encoders are suitable for diamond-turning and precision-grinding applications and for use in polishing equipment. They are available with various diameters and line-count options and are compatible with standard controllers. Digital quadrature outputs ranging from 27 arc sec to 0.01 arc sec resolutions are offered.