Question: Up to how far off can the Deal Timeball be from Coordinated Universal Time?

full_context: Document 1: Prime meridian (Greenwich): A prime meridian, based at the Royal Observatory, Greenwich, in London, was established by Sir George Airy in 1851. By 1884, over two-thirds of all ships and tonnage used it as the reference meridian on their charts and maps. In October of that year, at the behest of U.S. President Chester A. Arthur, 41 delegates from 25 nations met in Washington, D.C., United States, for the International Meridian Conference. This conference selected the meridian passing through Greenwich as the official prime meridian due to its popularity. However, France abstained from the vote, and French maps continued to use the Paris meridian for several decades. In the 18th century, London lexicographer Malachy Postlethwayt published his African maps showing the "Meridian of London" intersecting the Equator a few degrees west of the later meridian and Accra, Ghana.
Document 2: Big Ben Aden: Big Ben Aden (Arabic: بيج بن عدن‎ ‎ ) is a clock tower built by British engineers, along with locals, beside Aden Harbour in Yemen during the period that Aden Province (later called Aden Colony) was a territory within the British Empire. It is superficially similar to the Elizabeth Tower (popularly known as Big Ben), the famous clock tower attached to the Palace of Westminster in London. The clock was shut down for renovation about a quarter of a century ago, and returned to service in February 2012. The tower was built during the 19th century as part of the British colonisation of Aden Province, which began in 1839 and came to an end in 1967.
Document 3: Civil time: In modern usage, civil time refers to statutory time scales designated by civilian authorities, or to local time indicated by clocks. Modern civil time is generally standard time in a time zone at a fixed offset from Coordinated Universal Time (UTC) or from Greenwich Mean Time (GMT), possibly adjusted by daylight saving time during part of the year. UTC is calculated by reference to atomic clocks, and was adopted in 1972. Older systems use telescope observations.
Document 4: IERS Reference Meridian: The IERS Reference Meridian (IRM), also called the International Reference Meridian, is the prime meridian (0° longitude) maintained by the International Earth Rotation and Reference Systems Service (IERS). It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle or 102.478 m at the latitude of the Royal Observatory, Greenwich. It is also the reference meridian of the Global Positioning System (GPS) operated by the United States Department of Defense, and of WGS84 and its two formal versions, the ideal International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF).
Document 5: Greenwich Mean Time: Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London. GMT was formerly used as the international civil time standard, now superseded in that function by Coordinated Universal Time (UTC). Today GMT is considered equivalent to UTC for UK civil purposes (but this is not formalised) and for navigation is considered equivalent to UT1 (the modern form of mean solar time at 0° longitude); these two meanings can differ by up to 0.9 s. Consequently, the term GMT should not be used for precise purposes.
Document 6: Central European Time: Central European Time (CET), used in most parts of Europe and a few North African countries, is a standard time which is 1 hour ahead of Coordinated Universal Time (UTC). The time offset from UTC can be written as . The same standard time, , is also known as Middle European Time (MET, German: ) and under other names like Berlin Time, Romance Standard Time (RST), Paris Time or Rome Time.
Document 7: Swiss railway clock: The Swiss railway clock was designed in 1944 by Hans Hilfiker, a Swiss engineer, together with Mobatime, a clock manufacturer, for use by the Swiss Federal Railways as a station clock. In 1953, Hilfiker added a red second hand in the shape of a railway guard's signaling disc.
Document 8: Raymond Saunders (clockmaker): Raymond Saunders is a Canadian clockmaker who has designed and built more than 150 customized clocks that mainly serve as tourist-attracting public artworks. In 1977 he was commissioned to build a steam clock for the Gastown district of Vancouver, Canada. The Gastown clock may be the first steam clock ever built, although there is evidence that 19th century British engineer John Inshaw made a steam clock after which was named a Birmingham pub. Saunders has since built six different public steam clocks for clients such as the city of Otaru, Japan, and the Indiana State Museum. He has also built a clock for Vancouver's York House School's 78th birthday in 2010.
Document 9: Birgu Clock Tower: The Birgu Clock Tower (Maltese: "It-Torri tal-Arloġġ tal-Birgu" ), also called the "Vittoriosa Clock Tower" and originally the Civic Clock Tower, was a clock tower in Birgu, Malta. It was located in Victory Square, the city's main square, and it was a prominent landmark in Birgu and the rest of the Three Cities. The tower was probably built in the Middle Ages, although some sources state that it was constructed in 1549. It served as a watchtower since it had views over the Grand Harbour and the surrounding countryside, and it saw use during the Great Siege of Malta in 1565. A clock was installed in the tower in the 17th century.
Document 10: Deal Timeball: Deal Timeball is a Victorian maritime Greenwich Mean Time signal located on the roof of a waterfront four-storey tower in the coastal town of Deal, in Kent, England. It was established in 1855 by the Astronomer Royal George Biddell Airy in collaboration with Charles V. Walker, superintendent of telegraphs for the South Eastern Railway Company. It was built by the Lambeth firm of engineers Maudslay and Field. The time ball, which, like the Greenwich time ball, fell at 1 pm precisely, was triggered by an electric signal directly from the Royal Observatory.
Document 11: Clock Tower, Brighton: The Clock Tower (sometimes called the Jubilee Clock Tower) is a free-standing clock tower in the centre of Brighton, part of the English city of Brighton and Hove. Built in 1888 in commemoration of Queen Victoria's Golden Jubilee, the distinctive structure included innovative structural features and became a landmark in the popular and fashionable seaside resort. The city's residents "retain a nostalgic affection" for it, even though opinion is sharply divided as to the tower's architectural merit. English Heritage has listed the clock tower at Grade II for its architectural and historical importance.
Document 12: Greenwich Maritime Centre: The Greenwich Maritime Centre (GMI) is a part of the University of Greenwich. Established in 1998, it provides a specialist postgraduate and research institute within the large multi-faculty University of Greenwich. The aims of the GMC are to engage in and facilitate scholarly research, to disseminate and publicise research findings, to provide postgraduate teaching, to develop maritime education, to act as a forum for exploration of maritime issues, to serve as a source of expertise for business and government and to provide cost-effective consultancy services. The GMC provides an active centre for studying maritime history and is located in The Old Royal Naval College, Greenwich, across the road from the National Maritime Museum.
Document 13: DUT1: The time correction DUT1 (sometimes also written DUT) is the difference between Universal Time (UT1), which is defined by Earth's rotation, and Coordinated Universal Time (UTC), which is defined by a network of precision atomic clocks.
Document 14: Little Ben: Little Ben is a cast iron miniature clock tower, situated at the intersection of Vauxhall Bridge Road and Victoria Street, in Westminster, central London, close to the approach to Victoria station. In design it mimics the famous clock tower colloquially known as Big Ben at the Palace of Westminster, found at the other end of Victoria Street.
Document 15: Universal Time: Universal Time (UT) is a time standard based on Earth's rotation. It is a modern continuation of Greenwich Mean Time (GMT), i.e., the mean solar time on the Prime Meridian at Greenwich, London, UK. In fact, the expression "Universal Time" is ambiguous (when accuracy of better than a few seconds is required), as there are several versions of it, the most commonly used being Coordinated Universal Time (UTC) and UT1 (see below). All of these versions of UT, except for UTC, are based on Earth's rotation relative to distant celestial objects (stars and quasars), but with a scaling factor and other adjustments to make them closer to solar time. UTC is based on International Atomic Time, with leap seconds added to keep it within 0.9 second of UT1.
ground_truth: 0.9 s.