6.4 Unless the Parties have agreed otherwise in writing, CTC shall not be entitled to increase the Service Fee within the first three (3) Contract Years. Thereafter any increase of the Service Fee shall be limited to three (3) percent of the Service Fee p.a. and shall only be valid if one hundred and twenty (120) days [n.b. AMEND Clause 14.1 accordingly, if number of days is changed] Clause advance written notice has been given to Merck prior to the end of the then current Contract Year.