Words & illustrations by Andrew Emmerson

This is an 'entry level' guide to the subject, with links to resources on other websites.

Clicks and buzzes
What did people do before the speaking clock was invented if they wanted a time check? Simple: they rang the operator and asked her the time by the exchange clock on the wall, but this was not precise to the second, nor could the exchange always answer just when the customer wanted. The first genuine speaking clock machine was introduced in the USA in 1927, coming to Paris in 1933, The Hague in 1934 and Switzerland in 1935. But automatic time service (of a Heath-Robinson kind) had been available to telephone users in San Francisco since the late 19th century; by listening for to an observatory clock at least a minute and decoding clicks and single and double buzzes against some detailed instructions you could set a pocket watch - but it helped if you already knew more or less what the time was. A proper speaking clock is far more convenient...

The first British clock
The Speaking Clock service was inaugurated in London on 24th July 1936 with a pair of clocks in Holborn exchange (they had been developed by the Post Office Research Station at Dollis Hill, north London). A second pair of clocks was installed in Liverpool during 1942 as a safeguard against interruption, with a 'ring main' connecting both sets of clocks by diverse routes to all exchange centres in the country.


Two coloured photos of TIM taken from cigarette cards of the 1930s.
Source: writer's collection.


P4727 - the first speaking clock mechanism, which used photographic storage in revolving glass discs.
BT copyright image, used with acknowledgement.


P1280 - a technician adjusts the amplifiers of the first speaking 
clock mechanism; note Tele. 121 and Bellset 20 on the wall at rear.
BT copyright image, used with acknowledgement.

Click here for more pictures of the Speaking Clock

Here is a 'popular' description of TIM, taken from Practical Mechanics magazine, May 1938 (page 425)

A brief description of TIM the G.P.O. Clock, which has answered over 20,000,000 calls since its installation just over a year ago.

By William G. Pike - Talking Clocks are not new inventions, for clocks of this nature have been in use for a considerable time in Europe, Asia and elsewhere. There is nothing, however, quite like TIM, the wonder instrument of the Post Office. The sounds which come from this clock are recorded on glass discs, reproduction is remarkably clear and the discs are practically everlasting. Eighteen months' severe testing in the Post Office research station has resulted in the clock giving an extremely accurate performance. It is only possible, at present, to hear this clock in the London district, but it is hoped to extend the service to other   large towns in the near future. Proof of the popularity of this clock is shown by the fact that over 20,000,000 calls have been made since its installation a little more than a year ago. The public's appreciation of accurate time is evident, for 37,000 people asked the time between 8 a.m. and zero hour on the last Armistice Day.

Glass Discs
The main part of this ingenious clock consists of four circular glass discs like gramophone records. On each disc are photographed the various numbers and phrases as spoken into a special microphone by Miss J. Cain, who is now known as "the girl with the golden voice." The sound tracks, similar to those on the edge of a talkie, film, are arranged in a series of concentric circles.

Upon dialling the letters TIM a subscriber is connected with the clock and hears a voice repeating the time. The announcement is phrased as follows: "At the third stroke it will be ten, twenty-five and thirty seconds precisely" (or whatever time it is) followed by pip ... pip ... pip. The period of listening lasts from 1.5 minutes to 3 minutes, after which the call is automatically cut off.

Of the four discs, two share the minutes, each having thirty sound tracks. The other two discs are used for the hours and seconds. The hour disc has twelve tracks and the seconds disc six tracks. The various words of the sentences are also recorded on the various discs, so that when an announcement is made all the discs come into use.

Speech Reproduction
The reproduction if speech from the sound tracks is produced by focussing a ray of light on the discs and letting the light fall onto a photo-electric cell mounted on the opposite side. The electric current from the photo-cells is amplified, the volume of sound being such that two hundred people may listen at the same time.

The light rays are obtained from small electric lamps and a number of lenses. Each disc has its own lamp and set of lenses, usually referred to as the "scanners." The "scanners" are mounted on carriers which move in and out of the discs in order that the ray falls on the appropriate track. Movement of the "scanners" is governed by cams mounted on the carrier shaft. The cams work in conjunction with three ratchet wheels, one each for the hours, the minutes and the seconds, the ratchet mechanism being operated by trip magnets.

Extreme Accuracy
A very accurately controlled electric motor drives both the discs and the scanners. Extreme accuracy is ensured, for the motor speed is governed by a master clock having a free pendulum, beating seconds. Attached to the bottom of the pendulum is a slide having a number of transparent areas. Placed in front of the slide is an electric lamp, a series of lenses and a narrow vertical slit, and behind the slide is a photo­cell.

The current produced by the light falling on the photo-cell is amplified and used to give impulse to the pendulum. As long as the pendulum vibration. is constant, no impulse is given, but as soon as the vibration decreases, current from the photo-cell is used to increase the vibration to normal. In order that the error between the third pip and true time shall not be more than 0.1 second, the master clock is connected by relays to Greenwich Observatory, and synchronisation takes place every hour. Should the clock be out of step with Greenwich time, one of a number of relays is operated, causing the current in the coil of a magnet - which is placed beneath an armature fixed to the pendulum rod - to vary. By varying the force the rate of the pendulum can be advanced or retarded and brought into step

Two Clocks
Actually there are two clocks installed at the exchange. Erected side by side, both are running continuously. Should the first clock break down or have an error in excess of a tenth of a second from G.M.T. at any hour, the second clock automatically comes into action. The Post Office have spared no energy to make this service the most accurate possible, and they have been rewarded. TIM has already netted the sum of £85,000.

P4728 - the room where the first speaking clock was installed.
BT copyright image, used with acknowledgement

Full technical details of the Speaking Clock were given in an Institution of Post Office Electrical Engineers paper dated 27th October 1936. It can be downloaded here (warning: the file is 15MB long and is only on the CD).


Wartime developments

During World War II technology from the Speaking Clock was applied to other interesting projects. Special noise-cancelling microphones and headphones were devised by the Post Office for tank use. Deep below their Dollis Hill research station a special chamber with deafening sound effects was constructed to simulate a tank's interior.  Producing the sound effects with which to test these devices was another matter; recordings on 78rpm gramophone records would not last long enough and the chosen solution made good use of other Post Office technology.


First of all recordings were made - on direct-cut disk - of a tank rumbling past a microphone. Ten-second recordings made in this way were transferred to 35mm film by the Crown Film Unit (a new name for  the old Post Office Film Unit) and a two-second long section finally transferred to glass disc, for playing continuously on a speaking clock machine.


Apparently the joint in the recording and the two-second repetition were not noticeable in use. Similar machines were made for the Royal Air Force; these generated continuous background aircraft noise effects for training radio operators. Four different aircraft types were covered, at normal speed and at absolute maximum. Yet another machine was for training fighter pilots; this was a twin-channel simulator, providing continuous aircraft noise and spasmodic machine-gun effects as and when required.


Postwar developments

A replica of TIM using similar photographic soundtracks but with crystal oscillators for greater accuracy was produced in 1954.


New clocks using a revolving magnetic drum replaced the original speaking clock introduced in 1936. The 79 separate phrases required for a 12-hour clock were recorded as circular tracks spaced 1/16 inch apart along the length of the drum. The pips were not recorded on the drum but were derived from an oscillator. The Speaking Clock had accuracy to approximately 1/20 second. Like the first clock, the second speaking clock had its accuracy calibrated and corrected by referencing to a time signal from the Royal Greenwich Observatory, broadcast by Rugby Radio Station.


The Speaking Clocks in the Irish Republic and Channel Islands were seemingly not modelled on the British design. Ericsson Telephones Ltd described its own 'time announcer' product in the July 1962 issue of the Ericsson Bulletin and this may have been the product that these telephone administrations bought.


During the 1980s (possibly 1990s) BT renamed the Speaking Clock 'Timeline' but the name did not find much appeal.

In the 1980's British Telecom devised a solid state speaking clock known as Chronocal. It occupied a 19-inch rack cabinet about 3U (5.25") tall and could be equipped with either the Pat Simmons or Brian Cobby voices. The present digital system was introduced in 1984 and needless to say, this has no moving parts at all.


20,000,000 calls to TIM in the first year - 1936.

265,000,000 calls to TIM from London users from 1936 - 1949.
400,000,000 calls to TIM nationwide from 1936 - 1949.



Final of Golden Voice Competition for the Speaking Clock
The photograph shows the Postmaster General with judges who include Major Tryon and Mr John Masefield, the Poet Laureate (Picture dated 21 June 1935).



The voices of TIM
Jane Cane
- the first voice of the Speaking Clock voice. She was chosen after a nationwide competition among 15,000 women telephonists and was awarded ten guineas. Until then she used her first name Ethel but dropped this in favour of her middle name, Jane, and made a record for the GPO helping other staff improve their speaking voice. She went on to become announcer for Henry Hall during one of his broadcast concerts and was offered a film part by Columbia Pictures under the name of Jane Cain. Born 1st May 1909 - died aged 87 on 19th September 1996.

Miss Ethel Cain dialling TIM at Dollis Hill to hear her own voice tell the time, 20th March 1936.

Pat Simmons - A competition was held in 1963 to find a replacement for Miss Jane Cain's voice for the Speaking Clock.  It was won by Miss Pat Simmons, an Assistant Supervisor in Avenue Telephone Exchange, London.  She was to be heard until Brian Cobby replaced her in 1985.

Pat Simmons recording

Pat Simmons recording

Brian Cobby - The voice of the Speaking Clock today, he was interviewed and this is an extract:

How did you become the voice of the speaking clock?

I moved to Brighton more than 30 years ago and got a job with the Post Office, where I worked for 16 years. In 1984, British Telecom [as the Post Office's telephone arm became in 1981] decided to change the speaking clock. They ran a competition among the staff to find a replacement voice, which had to be clear and warm with no regional accent. After a series of regional heats, I beat a lady from Lowestoft in the final. She became the voice that says, "the number you have called has not been recognised." I became the voice of the speaking clock on 2 April 1985 at 11am, precisely. The telephone lines were jammed with people trying to listen.

How long did the announcements take to record?

Just an hour, but it was hard work. I recorded the times in a studio in London, where I had to read from a 33-page script. It was calculated mathematically [only 86 words are actually used], so I didn't have to go all the way round the clock. Later, we found that we hadn't taped the 'o' clock' so I had to drive back up to London just to record that.

Might we have heard your voice anywhere else?

Maybe. Before I worked for BT I was an actor. As well as films and some Shakespeare, I did a lot of voiceover work, mostly for commercials. In 1965, I did one of my most famous voiceovers: the countdown for the TV programme Thunderbirds.

The poster above them looks intriguing...

Yes, it's from a 1959 film I did, called The Nudist Story. It was billed as being shown in 'blushing technicolor'. Many years later, a Sunday paper ran a story, 'Speaking clock in nude movie'. The picture they printed of me was actually that of a boy who played my brother, who, alas, was a lot skinnier than me. I had a great body in those days...

The wording of Brian Cobby's announcement was altered in 1986 to include the phrase "sponsored by Accurist " to become "At the third stroke the time sponsored by Accurist will be...."

Lenny Henry - Lenny Henry is to provide the voice of the speaking clock for the next fortnight. The comic's Black Country burr will replace the usual plummy tones of BT's service as part of a Comic Relief fundraising drive. Callers dialling 123 pay will 10p for the service, and proceeds from today to March 23 are expected to raise £200,000 for the charity. Lenny, who is temporarily replacing Brian Cobby as the voice of the clock, is only the fourth ever person to take on the role in its 67-year history. He will be putting on a different voice each day in the hope of encouraging people to ring back. He said: "I can hardly believe it. Wait until you hear what we've done to the pips." March 10, 2003

Alicia Roland - A 12-year-old girl says she is proud to have become the only child and the first Scot to record the Speaking Clock in its 67-year history. The schoolgirl's voice will be heard by up to two million callers over the next week. Alicia, from Brookfield, Renfrewshire, beat thousands of children from all over the UK in a competition to become the voice for a week. The idea is part of the Big Listen, a week of activities which encourages adults to listen to young people and raise money for the charity ChildLine. Organisers estimate Alicia will raise £200,000 during her week in the job - calls cost 10p and BT is donating every penny to the good cause. She said: "It's very nice to be the first child to do this job, I think it's good for people to hear a child's voice when they ring up. "My friends at school were a wee bit envious but they've been really supportive, they said they're going to ring up the clock loads this week."  It is only the fifth time that the Speaking Clock - which began in 1936 and receives 80 million calls a year - has been changed. 13th October 2003

Dialling codes
The original dialling code was TIM, short for Time, which was used in London and other major cities. At smaller locations the code was 8081 or 9-8081. After the change to all-figure numbering at the end of the 1960s the TIM code was changed to 123 and elsewhere 8081 was changed to 123 also, some time in the 1990s. 

The accuracy of the speaking clock is beyond reproach, within five thousandths of a second in fact. With a built-in crystal oscillator and microprocessor logic control, the complete apparatus is  made of solid-state microchips and occupies no more shelf space than a small suitcase does. Contrast that with the array of motors, glass discs, photocells and valves of the original speaking clock back in 1936 - it took up most of the floor space of a small room!

Major organisations such as Network Rail and London Weekend Television have permanent feeds of the clock from BT into their private internal phone systems so employees can check the time without making an outside call. The timing of all ITV television programmes is synchronised to TIM as well, so when your local station goes over to ITN for the News at Ten, this is done "at the third stroke". And perhaps the strangest - and certainly longest distance - call to the British speaking clock is from the factory in Hong Kong that which makes the handsets for  the new VideoPlus VCR programming system. The in-built clock is set to British time, courtesy of BT's Timeline service.

Update, by James Campbell (January 2001)
A direct feed existed to the BBC. I remember in about 1983 visiting a BBC building on the Embankment just round the corner from Westminster tube station, it was no 1 (can't remember the name of the road). It was a half derelict building covered in pigeon sh*t, but on the second floor was the BBC Parliamentary Recording Unit. It was linked via cables under the road to the Houses of Commons and Lords. This was a place that looked like a museum but was fully operational. The thing that I found amusing was the fact that they recorded all the material in mono on one track of the tape recorder, and recorded TIM on the other track as a quick time reference. Because the pips were rather good at breaking through to the other speech track, this particular TIM, provided by BT, did not have any pips and was known by the BBC as "seedless TIM".

What's left to see or hear of the old clocks
Not a lot is the simple answer. The Australian clock of 1954 used to be on display at the Science Museum in London but after falling into disrepair.  One of the original TIM clocks was preserved and was donated by British Telecom to the British Horological Institute's museum at Upton Hall near Newark, but this too is not in working order.   People report having heard the Pat Simmons speaking clock (thanks to TIM 2000) on the following numbers: (0870 765) 8081, (0845 092) 8081, 0845 124 9068 and (0131) 477 7676.

The above numbers may not be accurate so try 01352 838081 and 01286 868081.

TIM 2000
In the year 2000 a project was devised for creating a compact electronic speaking clock (with the Pat Simmons voice). Around 75 units were sold (there are no plans to make any more). For more information see  http://www.samhallas.co.uk/repository/tim_2000/

Further reading

  • The Post Office Speaking Clock in Practical Mechanics, June 1936 (pp 514-515).
  • The GPO Speaking Clock in Practical Mechanics, May 1938 (p 425).
  • The Speaking Clock of Paris in Practical Mechanics, April 1934 (pp 317-318).
  • The New Speaking Clocks in The Post Office Electrical Engineers' Journal, April 1963 (pp 1-6).

Further resources on the WWW


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Last revised: January 30, 2021