Backward and forward
The 'right time' was standardised across Britain and Ireland in the 19th century to solve the railway companies' dilemma of trying to devise timetables for routes that began and ended in locations with varying 'local times'.
GMT was introduced across Britain in 1880, but Ireland retained its own official time zone until 1916.
This was based on Dublin Mean Time, calculated on the 25-minute difference between Dunsink Observatory and Greenwich.
Before Dublin Mean Time was declared by the 1880 Time Act, the clock varied across Ireland with the official time in Cork, for example, 11 minutes behind Dublin, while Belfast was over a minute ahead.
The present system of 'daylight savings time' or 'summer time' across Britain and Ireland was also introduced in 1916.