Chemical polarimeters measure the "optical rotation angle" of materials, i.e. their ability to rotate linearly polarised light. They are essential analytical tools in many fields including pharmaceuticals, food, cosmetics and chemicals. Conventional polarimeters work by aiming a vertically polarised laser beam at a horizontally oriented polariser which blocks the incident light. Placing an optically active sample in the path of the laser beam causes the polarisation axis of the beam to rotate, allowing some of the laser light to leak through the polariser. The polariser is then rotated until the leak is eliminated, and the optical rotation angle is found by measuring the angle through which the polariser has been turned. The technique is simple in theory but rather challenging in practice since it requires precision optics, sensitive detectors, high-quality motors, and accurate rotary sensors capable of measuring angular deviations of just a few millidegrees. Consequently, high resolution commercial instruments are expensive, typically retailing for US$10000 -US$30000.