Evolution of the partial gas pressures is coupled to the operation of the different pumping systems as follows: i) the valve connecting the IGP to the main chamber is closed after 175 s; ii) in addition the TSP valve is closed after 315 s; iii) the TSP valve is opened after 575 s; iv) the IGP valve is opened after 705 s; v) the TMP valve is closed after 895 s; vi) the TMP valve is opened after 1067 s.