Instrumental asymmetry in the COMPASS experiment COMPASS studies the nucleon spin structure via the determination of the spin dependent properties of semi-inclusive deep inelastic scattering. This entails the measurement of the counting rates asymmetry between 2 different spin configurations of the experimental setup, derived from one another by reversing the sign of one its magnetic field. The proposed project is to study the impact of various instrumental aysmmetries on this measurement. A basic one arises from the top/bottom asymmetry of the tracking system when the cross-section depends upon the azimuthal angles of the two particles required in the semi-inclusive final state. Its impact on the measurement will be studied by Monte-Carlo simulations of the experiment