Optical Lever Calibration of Cap Sensor The capacitance angle sensor, while very convenient for electronic read-out and also very precise, is not particularly accurate. Hopefully, you recall the difference between precision and accuracy. We can calibrate the sensor using an "optical lever", which is very accurate AND sensitive, but not so convenient. The optical lever is implemented by directing a laser beam onto a small mirror attached to the boom. The reflection is viewed on a distant wall, giving very high angular sensitivity. Note that a boom deflection of ? provides a beam with deflection of 2? . You will need the distance from mirror to wall, which is L = 755 +- 2cm. It is also helpful to know the fiducial (zero reference angle). This is conveniently obtained from the laser reflection from the front (plastic) window, which corresponds to ? =0 by construction. You can find that point from the image LaserCalib_Wide.jpg. The fixed spot is far below the moving spot, so you'll need to estimate the horizontal position as best you can. The angle then is given from tan(?) = x/L, where x is the horizontal distance from the fiducial.