the large hall. In the 1847 station, bells rang before each departure of the Spanisch-Brötli-Bahn. The signal order prescribed as follows: "10 minutes before the departure of a train, one [bell]; 5 minutes before the same, two [bells]; and immediately prior to departure, three bells". For the 1871 renovations, the architect Jakob Friedrich Wanner gave the station clock the place of honour in the portal above the main entrance, and the bells were placed in a small tower in the east facade. On 12 September 2006, to commemorate the station's 150th anniversary, the ETH Zürich installed the NOVA, a three-dimensional, bivalent display, which consists of 25,000 individually addressable light balls. It represents a play of light of several colours, but can also represent cinematic sequences. It is expected to remain hanging in the station until further notice. Operation Zürich HB is served by more than 2,900 trains daily. In 2018, it had an average of 471,300 passengers each working day. The station is busy at all times, with trains running from 05:00 until 01:00 during the week. From Friday night to Sunday morning, trains run all day and all night as part of the ZVV Nachtnetz (night network). Tracks The station has four distinct groups of tracks, giving a total of 26 tracks: Tracks 3 to 18 are terminal tracks located at ground level, served by two side platforms and seven island platforms. These are used by long-distance trains from throughout Switzerland, and by international trains such as the EuroCity, Cisalpino, InterCityExpress and TGV. Tracks 21 and 22 are underground terminal tracks, served by a single island platform, and located on the southern side of the station. This platform is known as and is used by SZU S-Bahn trains, heading west and south towards Uetliberg and the Sihl valley. Tracks 31 to 34 are underground through tracks, served by a pair of island platforms, and located just to the north of tracks 21 and 22. These are used by long-distance and S-Bahn trains running to and from Oerlikon station via the Weinberg Tunnel. Tracks 41 to 44 are underground through tracks, served by a pair of island platforms, and located on the northern side of the station. These are used by S-Bahn trains running via the Hirschengraben Tunnel and Zürich Stadelhofen station. International services The following international services call at Zürich Hauptbahnhof: Intercity Express: four round-trips per day over the