GB1275693A - A clock for indicating the local time at different places throughout the world - Google Patents

Abstract

1275693 Geographical time indicating DAINI SEIKOSHA K K 7 Aug 1970 [20 Aug 1969] 38224/70 Heading G3T A digital display world clock which can selectively indicate time expressed as - day, hour, minute, second corresponding to each major city in the world includes a clock pulse generator 1 Fig. 1, comprising a quartz crystal oscillator and frequency divider and which in normal operation feeds a 1 Hz signal to a 'seconds' portion of a digital counter 2. The counter produces a reference signal representing a reference time and which increases at the rate of one/sec in synchronism with elapsing time. The units of min. and sec. components are fed direct to a visual display indicator 7 while the date, hour and tens of minutes components of the counter output are fed to the display 7 via an adder 6 where they are added to a time difference signal corresponding to any particular city selected by means of a switch 8. Since the time zones around the world differ in multiples of 30 mins. it is not necessary to adjust the mins. and secs. indications. When not required to indicate time at other places, the counter can supply a count indicative of local time. The reference time may be Greenwich Mean Time minus twelve hours. Correction for "summer time" can be effected by operation of a switch 9 whereby to add a further difference signal of one hour. A switch 3 is operable to adjust for the number of days in the month. For fast adjustment of the reference signal to a value equal to the reference time, the switch 4 is moved so as to apply the 1000 Hz or 100 Hz pulse trains to the minutes counting portions of the counter 2. The digital display indicator may comprise electron valve or semi-conductor numerical display units.