20 On Northfields station, London Underground changed its requirements late in the construction phase. In October 2004, three months before completion of the work, London Underground requested the revision of plans for station operations room windows and doors. Tube Lines estimates these changes added 35 to 50 days to the construction time, because a new manufacturer had to be contracted to provide the revision. London Underground also suggested that ATMs be installed in the station. According to Tube Lines, this request caused "turmoil with respect to the ongoing construction works", because of necessary revisions of design and construction plans. Both revisions were made in accordance with the PPP contract and Tube Lines still managed to deliver on time.