A measurement method for the determination of the cell parameters of vertically aligned nematic LCOS devices has been developed. It provides the values for the pre-tilt angle and the cell thickness in a reliable way, without the need for spectroscopic instruments. The method uses oblique incidence to separate the determination of pre-tilt angle and cell thickness from each other and thus enhance the measurement accuracy. As a bonus, the measurement system consists only of simple optical components and does not need costly instruments.