Method to accurately measure both refractive index and the thickness of glass is investigated. The method combines equal inclination interference with dispersive interferometry. The interference signal, which is detected by the spectrometer, contains different frequencies and can be demodulated with high accuracy. The experiments indicate that the standard deviation of the thickness is better than the 35 nm, while the standard deviation of the measured refractive indices is below 5.76 × 10-6. Furthermore, absolute angles, between 0° and 51°, can be measured with a repeatability within 5′.