1 . AGRICULTURE - COMMON ORGANIZATION OF THE MARKETS - DISCRIMINATION BETWEEN PRODUCERS OR CONSUMERS - PROHIBITION - SCOPE - ADDITIONAL LEVY ON MILK - CHOICE OF REFERENCE YEAR BY THE MEMBER STATES - DISCRIMINATION ARISING BECAUSE OF THE CHOICE MADE BY A MEMBER STATE - NOT PERMISSIBLE ( EEC TREATY , ART . 40 ( 3 ), SECOND SUBPARAGRAPH ; COUNCIL REGULATION NO 857/84 , ART . 2 ( 1 )) 2 . AGRICULTURE - COMMON ORGANIZATION OF THE MARKETS - MILK AND MILK PRODUCTS - ADDITIONAL LEVY ON MILK - DETERMINATION OF REFERENCE QUANTITIES EXEMPT FROM THE LEVY - CHOICE BY A MEMBER STATE OF 1981 AS THE REFERENCE YEAR - WEIGHTING PURCHASERS ' REFERENCE QUANTITIES ACCORDING TO DELIVERIES OF CERTAIN CATEGORIES OF PERSONS LIABLE FOR THE LEVY - PROHIBITION ( REGULATION NO 804/68 OF THE COUNCIL , ART . 5C ; COUNCIL REGULATION NO 857/84 , ART . 2 ( 1 ) AND ( 2 )) 3 . COMMUNITY LAW - INTERPRETATION - METHODS 4 . AGRICULTURE - COMMON ORGANIZATION OF THE MARKETS - MILK AND MILK PRODUCTS - ADDITIONAL LEVY ON MILK - CHOICE OF FORMULA B - INDIVIDUAL REFERENCE QUANTITY OF A FARMER WHO HAS CEASED PRODUCTION - ADDITION TO THE NATIONAL RESERVE ( COUNCIL REGULATION NO 857/84 )