++++ FREE MOVEMENT OF PERSONS - MIGRANT WORKERS - OLD - AGE AND DEATH ( PENSIONS ) INSURANCE - PENSION RIGHTS RELATING TO ACTUAL INSURANCE PERIODS ASSIMILATED BY VIRTUE OF THE LEGISLATION OF DIFFERENT MEMBER STATES - CALCULATION OF BENEFITS ON THE BASIS OF DIFFERENT UNITS OF COMPUTATION IN EACH STATE - CONVERSION INTO A UNIFORM UNIT FOR THE PRO RATA CALCULATION