During the century since 1884 there have been fundamental changes in the principles on which timekeeping is based; nevertheless, almost all countries now base their civil timekeeping on a time scale which is the standard time of the Greenwich meridian and which remains within 1 second of the time envisaged at the Washington Conference. The system of time zones, in which universally valid hourly markers were given longitude-dependent labels, spread rapidly under the influence of the railway systems, with legislation usually following established practice. Daylight saving time, first introduced in many countries in 1916, is a form of mass self-deception which provides extended summer evenings in the temperate zones but causes inconvenience to the travel industry and confuses its customers.