17 Tariffs clearly show the telecommunications networks and services which are offered, how tariffs are calculated for each network and service, and the actual tariffs for the network or telecommunications service or for each unit of time for which the telecommunications services are offered. Tariffs for dominant organizations are based on objective criteria and on the costs of providing the public telecommunications network and service together with a reasonable rate of return. Public telecommunications operators may set different tariffs for different times of the day (price regulation depending on hours). Tariffs for access to and use of public networks are independent of the use to which the user puts the network except in cases where different services or facilities are required. Tariffs are set out in clear and sufficient details and are sufficiently unbundled, such that a user of public networks or public telephone services is obliged to take or pay for any facilities that are not required. No public telecommunications service tariffs discriminate, between users but public operators have the right to introduce: 1° discount schemes for users which are directly related to the user’s volume of traffic either overall or to specific numbers; 2° special tariffs for users making little use of the public telecommunications services during hours in which those networks are not frequently used; . 3° special tariffs for defined disadvantaged groups of users. The public telecommunications operators must inform the Regulatory Board of those schemes, and any changes made to these at any time. The Regulatory Board may at any time require dominant organizations to implement special tariffs provided for in paragraph (7) 2° and 3° of this Article. No tariffs or changes to these or discount schemes can come into effect before a period of 30 days from the date of their publication is ended. No tariff or discount scheme can contain: 1° any discounts which create prejudice competitive opportunities of other telecommunications organizations in any particular telecommunications market; 2° any surcharges which can be levied solely because the public telephone operator is a dominant organization; 3° any differences for a user or users in different parts of the geographic area covered by a public telecommunications operator, unless there are objective reasons that justify such differences which are approved by the Regulatory Board.