Ellipsometry is particularly attractive for its suitability for in-situ measurements and remarkable sensitivity to minute inter-facial effects, such as the formation of sub-monolayer of atoms or magneto-optical (MO) effect. MO methods have been established as a common technique for studying thin film and surface magnetism. Ellipsometric setups with a photo-elastic modulator are favored for its high signal to noise ratio. One of the objectives of this work was to calculate the posibility of magneto-optical Kerr effect measurements with all optical devices in one branch of the setup fixed. This would allow for better noise cancelation in fixed branch. Common way of obtaining equations for a data analysis is a direct derivation from Jones or Mueller matrices of the system for each way of measurement separately. In spite of their various advantages the general scalar equations of the setup are not being used. General equations allow easy calculation of each component’s imperfection influence on the results as well as quick derivation of all ways of measurement possible. Minor alteration of Jones formalism is proposed here that takes further advantage of the symmetry and allows for easier derivation of general analytical equations for the first and the second harmonic and DC signal. Novel nulling method for MOKE measurements is calculated and experimentaly prooved that offers better precision in desired region of measurment and reduces moving parts to a single branch of measurement setup. The only trade-off of the proposed method is slightly more complicated nulling procedure. Furthermore an automatic calibration of spectral magnetooptical Kerr effect measurement setup was designed and applied.