Interferometric measuring method and apparatus

Method in which frequency modulated light is generated and directed at a surface to be measured and a reference surface. The resultant light is combined to form an interference pattern that is measured by a photo-detector. Object surface distances are measured using the phase of the photo-detector signal (Ph) with the phase measured at at least two different time points together with the wavelength corresponding to the frequency modulation at those two points. The resultant measurements are evaluated. The invention also relates to a corresponding interferometer measurement arrangement.