This disclosure provides systems, methods and apparatus, including computer programs encoded on computer storage media, for measuring a distance. In one aspect, the method includes actuating or releasing an interferometric modulator having a first surface and a second surface and measuring a distance between the first and second surfaces at a plurality of times during the actuation or release. In another aspect, the method includes illuminating, with a first laser beam having a first wavelength and with a second laser beam having a second wavelength different from the first wavelength, an interferometric modulator having a distance between a first surface which is at least partially reflective and a second surface which is at least partially absorptive, measuring a first intensity of the first laser beam modulated by the interferometric modulator and a second intensity of the second laser beam modulated by the interferometric modulator, and determining the distance based on the measured intensities.