Indian Standard Time

Today Indian Railways, and indeed, everybody and every agency in India, observe Indian Standard Time (IST), which is defined as being 5 hours and 30 minutes in advance of UTC (formerly GMT) -- and hence also denoted as UTC+0530. In certain time-zone maps, IST is also designated E*. There is only one time zone for all of India. India does not observe any form of daylight saving time or any other seasonal adjustments to the time.

In the very early days of railways in India, local time was observed at each large city, in common with practice in most other countries at the time. Because of their importance as commercial and economic centres, Bombay time and Calcutta time assumed special importance and were followed for many official purposes in the late 19th century (Bombay Time from 1884), effectively forming two time zones for British India. Calcutta time was 5 hours, 30 minutes, and 21 seconds in advance of GMT, while Bombay Time was 4 hours and 51 minutes ahead of GMT. However, many railway companies standardized on using Madras time as being in between Bombay and Calcutta times, and often this, rather than Bombay time, was what was used in Indian timetables from the late 1880s onward, including the Newman's Indian Bradshaw, although this was far from universal.

In 1884, the World Meridian Conference at washington, DC, in the USA, set up the standard time zones as we know them today. Sandford Fleming, a Canadian, is generally credited with the proposal, although American and Canadian railways had by then already been observing standard time based on hour-wise time zones proposed by Charles F Dowd in 1863. It must be noted that the standardization of time zones was quite heavily promoted by the railway companies of the time in the United States and elsewhere because of the confusion and complexity of keeping track of local times in many different cities. British India did not adopt the standard time zones, however, until 1905 when the meridian passing through Allahabad at 82.5 degrees east longitude was picked as the central meridian for India, corresponding to a single time zone for the country at 5 hours and 30 minutes in advance of GMT. This went into force on January 1, 1906. (Also for Sri Lanka, then Ceylon.) However, Calcutta time was officially maintained as a separate time zone until 1948. Bombay time was maintained, but only informally (although used for some railway purposes too), until about 1955.

After independence and the partition of British India, Pakistan stayed on Indian Standard Time for three years and adopted Pakistan Standard Time at 5 hours in advance of GMT in 1951. In India today, official time signals are generated by the Time and Frequency Standards Laboratory at the National Physical Laboratory for commercial and official use, and is based on atomic clocks. These clocks are tied into the world-wide system of clocks that support UTC or Universal Coordinated Time.

In the 19th century, timekeeping by the railways was by means of standard-issue pendulum clocks at stations and of course, the iconic station master's watch or timepiece. The clocks at different stations, at least the bigger ones, were generally kept in fair synchronization by telegraphic means -- a time signal was sent from the head office or the regional headquarters of a railway at a specified time every day, and the station clock was to be adjusted appropriately.

This allowed trains to be run according to published timetables without the confusion of accounting for myriad local times. (This is a system that is based on the one developed in the UK in 1852, in which time signals were sent telegraphically from the Royal Observatory at Greenwich to various railway stations.) Four o'clock was a common time of day when the time signals were sent from the control office. The control office of course maintained its own principal clocks which kept official time for the railway.

By the turn of the century, all main-line stations were in telegraphic communication and thus could synchronize their clocks in this way to the official time. The convention developed of having the signals department of a railway be in charge of the chronometry and uniform timekeeping. Around 1925 omnibus telephone systems and train control circuits developed which further improved the synchronization of station clocks. Around 1952-1954 the railways generally shifted to a divisional system of working where the principal clocks were maintained at divisional headquarters instead of at the regional headquarters or head offices.

A significant development in the 1940s, especially after 1947, was the use of radio by the government and by commercial concerns, to broadcast time signals for various purposes. In the second half of the 20th century, the use of the time signal at 1600 hours generally fell into disuse and stationmasters and other staff were generally free to set their clocks according to the widely available radio time signals from broadcast stations.

From about 1952 onwards, drum clocks working on the electric mains supply became common in many stations, especially the suburban stations in Bombay. These clocks used a multi-polar hysteresis armature motor which, when excited by the 50Hz mains supply produced a low rpm output for use in the clocks. The first such clocks appeared at Churchgate, Bombay Central, and some WR suburban stations. Victoria Station and some other locations, on the other hand, used the 'Pulsynetic' pendulum clock (by Gents of Leicester, England) which could drive a number of half-minute slave dials.

Drum clocks and others relying on the stability of the 50Hz AC mains supply did have some problems as the frequency of the supply did occasionally vary when power plants came on line or went off the grid. This led to some of the station clocks being off by a couple of minutes or more in a day on occasion. This led to the practice of creating a separate special local supply of the 50Hz AC for important stations such as Churchgate, from about 1974 onwards. The 50Hz AC supply unit consisted of a DC-to-AC converter run from a crystal-controlled oscillator output divided digitally to produce a 50Hz 230V supply. Clocks run on this supply at Churchgate had errors of 1 second in 8 days. This system was adopted widely at many stations for maintaining the clocks' accuracy without manual intervention. In recent years, with the falling prices of electronics, crystal-controlled (quartz) digital clocks have been introduced with extremely good accuracy. Synchronization -- as needed -- is achieved by means of a special ring on the control telephones for all station masters in a given division at a chosen time -- often 0000 hours. Some stations are now experimenting with installing GPS-based clocks that keep time in synchronization with the GPS satellite signals.

Of course, while the running of trains generally does not require accuracy in timekeeping to better than a few seconds at best, the more recent rise of services such as GPS for location tracking and geospatial services has necessitated the use of extremely accurate timekeeping systems (which may be encapsulated today in fairly inexpensive handheld GPS receivers and other devices!), which ultimately rely on precise synchronization with UTC.