A voice announces:
"At the third stroke, the time will be (hour) (minute) and (second) seconds"
For times that are an exact minute, "precisely" is substituted for the seconds portion of the announcement
Similarly, announcements for times between the hour and one minute past the hour substitute "o'clock" for the (zero) minutes
Other operators run their own speaking clocks, with broadly similar formats, or redirect to BT's service.
A speaking clock service was first introduced in Britain on July 24, 1936
The mechanism used was an of array of motors, glass discs, photocells and valves which took up the floorspace of a small room
The voice was that of London telephonist, Ethel Jane Cain, who had won a prize of 10 guineas (£10.50) in a competition to find the right voice
Cain's voice was recorded optically onto the glass disks in a similar way to a film soundtrack
The service was obtained by dialling the letters TIM (846) on a dial telephone, and hence the service was often colloquially referred to as "Tim"
However this code was only used in the telephone systems of the cities of London, Birmingham, Edinburgh, Glasgow, Liverpool and Manchester
Other areas initially dialled 952 but with the introduction of Subscriber Trunk Dialling it was changed to 80 and later 8081 as more 'recorded services' were introduced and was standardised to 123 by the early 1990s.
The time announcements were made by playing short, recorded phrases or words in the correct sequence
In an interview with Manchester Radio in 1957 Miss Cain said:
The way I recorded it was in jerks as it were
I said: "At the Third Stroke" (that does for all the times), and then I counted from One, Two, Three, Four, for the hours, we even went as far as twenty-four, in case the twenty-four hour clock should need to be used, and then I said "...and ten seconds, and twenty seconds, and thirty, forty, fifty seconds", and "o'clock" and "precisely"
The famous "precisely"
So what you hear is "At the Third Stroke it will be one, twenty-one and forty seconds".
In 1963, the original device was replaced by more modern recording technology using a magnetic drum
This system gave way to the present digital system in 1984, which uses a built-in crystal oscillator and microprocessor logic control