International Meridian Conference
On 11 October 1883, a convention of railroad executives met in Chicago and agreed to the implementation of five time zones in North America, using as a basis Greenwich Mean Time. Before the invitations to the Washington conference were sent out on December 1, the joint efforts of Abbe, Fleming and William Frederick Allen, Secretary of the US railways' "General Time Convention" and Managing Editor of the "Travellers' Official Guide to the Railways", had brought the US railway companies to an agreement which led to standard railway time being introduced at noon on 18 November 1883 across the nation. Although this was not legally established until 1918, there was thus a strong sense of "fait accompli" that preceded the Washington conference, although setting local times was not part of the remit of the conference.
Time in New Zealand
In 1941, during the Second World War, clocks were advanced half an hour, making New Zealand 12 hours ahead of GMT. This change was made permanent from 1946 by the "Standard Time Act 1945", at which the time at the 180°E meridian was made the basis for New Zealand Time. NZST remained half an hour ahead of NZMT, and the Chatham Islands 45 minutes ahead of NZST.
In the late 1940s the atomic clock was developed and several laboratories began atomic time scales. A new time scale known as Coordinated Universal Time (UTC) was adopted internationally in 1972. This was based on the readings of atomic clocks, updated periodically in accordance with time variations in the Earth's rotation by the addition or deletion of seconds (called leap seconds). The "Time Act 1974" defines New Zealand Standard Time as 12 hours in advance of UTC.