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Using the technology

Baudot distributor and keyboard - Connected Earth artefacts, now at the Amberley Museum

Baudot changed : sense of rhythm required

The Baudot system was potentially fast, using multiplexing and code groups - but the original keyboard was very difficult to use.

There were five 'piano' keys, worked with two fingers of the left hand and three of the right. The keys were pressed down in varying combinations that represented a character in 'Baudot 5-unit code'

Operating this system required a lot of skill - the operator had to keep up a steady unvarying rhythm of about 150 letters per minute.

Eventually the system was replaced by new 5-unit systems.

Picture demonstrating use of a dial

The telephone dial : from a quick request to a slow pulse

In the early days of the telephone there was no need for a dial at all. Picking up the telephone connected you direct to the operator, who then connected you through to the number you asked for.

Later, automatic exchanges used electro-mechanical switching systems. Your telephone needed to send a series of electrical pulses to the exchange to tell it the number you wished to call, and the technical solution was the rotary dial.

When you dial a number and let go, a spring rotates the dial back to its original position. As each number is dialled, the mechanism sends that exact number of electrical signals to the exchange.

The signals sent are often referred to as 'pulses', but they are actually 'breaks'. In other words the dial switches off and on a steady electric current flowing in the line from the exchange. As this happens, the exchange senses the current stopping and starting, and decodes the digit dialled - one 'break' for 1, two 'breaks' for 2, and so on up to ten 'breaks', sent by dialling the digit '0'.

Lettered dial face

Adding letters to the telephone dial : a number to remember

Electromechanical switching systems such as Strowger worked by routing calls step-by-step through a sequence of electrical switches, all the way to the number being called. For what are known as 'own exchange' calls, all this happens with a single telephone exchange, but most calls need connecting through to other exchanges, and many pass through intermediate exchange along the way.

From the late 1920s onwards, Britain's major cities needed seven-digit numbers, consisting of three digits to identify the exchange frequired, ollowed by four digits to identify the individual telephone line on that exchange.

But these long numbers were thought to be too difficult to remember, so the number was 'repackaged' in a mixed form with the exchange digits element as the first three letters of the exchange name. So, for example, the number 1234 on London's 'Arnold' exchange was quoted as ARNold 1234.

This greatly improved user convenience, even though it did mean having to include the letters in the dials.

Lorimer wall telephone - a Connected Earth artefact, now in the Milton Keynes Museum collection

Alternatives to the dial (1914) : it could have looked like this ...

The very first automatic telephone systems made by Almon Strowger used a trio of push buttons to signal numbers being called. This was fine when telephone numbers had only three digits, but the telephone dial was a more convenient way to send longer numbers.

By 1912, the dial had become the standard way of operating mechanical switching, and was fitted to most of the different systems tried by the GPO, including Strowger, Relay Automatic, and Rotary systems.

The significant exception was the Lorimer system developed, installed in Hereford in 1914. From Canada, Lorimer telephones used four levers to set the numbers and a crank handle to send these digits once the levers had been set.

The method was supposed to be less prone to dialling errors - but that wasn't much of a problem in any case. In every other respect the Lorimer system was too limited and complicated to succeed. It was also not exactly confidence building - you could be happily chatting to someone only to find yourself connected to another number halfway through the call!

Trimphone advertisment, showing later keypads, 1980

Pushing buttons : more push - less pull

From around 1970 push button phones made dialling numbers far easier. That was because the dialling process was much shorter - punching out a sequence of numbers rather than having to turn the dial and let it spin back so many times.

Mechanically, though, the process was hardly any quicker - because each button push was actually generating a series of pulses to go down the phone line, no faster than those produced by a rotary dial.

It required the introduction of electronic exchanges from the mid 1970s onwards to recognise tone dialling - each button generating a different pair of musical tones.

This was faster, more accurate - and compatible with other electronic equipment. From here onwards, it became possible for machines and systems to do your dialling for you.

Telephone and Calculator keypads

Keypad design : a different set of values

People sometimes wonder why telephones and calculator keypads have different number layouts. The reason is quite logical - they were developed for different purposes. The calculator keyboard is a carry-over from the old adding machines used by trained operators, where the layout was designed to minimise the operators' finger movements, with the lower (more frequently used) keys and zero within easier reach than the higher numbers. The keyboard also follows mathematical convention, with a numbering range from 0 (zero) to 9.

When push button telephones were introduced most people had never seen, let alone used, a calculator, meaning that the keypad layout could be optimised for telephone users. So today's keypad layout is the result of comprehensive testing for the human factors involved, carried out by the Post Office in the 1960s and 1970s.

Human factor trial keypad telephones. Most retained the same sequence of digits as on the dial - 1 to 0, but not all. One (bottom left) had the digits running 0 to 9, from bottom to top right. These Connected Earth artefacts are now at the Amberley Museum

Keypad telephones used in human factor trials (1960s) : the soft touch

Keypad telephones offered a quicker and simpler way to make a call but, when the telephones were being developed, no one was sure what the best layout for the buttons would be.

The dial telephone had been around for decades and the slow speed of dialling, with callers forced to wait for the dial piece to spin back to rest between every number was a hindrance to the increasingly long numbers being dialled. The keypad offered many benefits, but it needed to fit inside the space previously occupied by the dial.

These telephones show four different trial layouts. They were used in intensive laboratory and user tests and, if you want to know the results, just look at the layout on your telephone now.

Just as on the dial, the digits run from 1 to 0, unlike the numbers on computers and calculators, which run from 0 to 9 - the other way around - for different reasons.

Dial of Destiny (1920s) : for the executive who has everything

Place the mouse over the QuickTime image. Left-click and drag either left or right to rotate the animation.
Dial of Destiny 3d object

The Dial of Destiny was the rather grandiose title given to what was basically an executive gift.

Public Relations had not reached the developed art that it is today - nevertheless, manufacturers still appreciated the value of building good customer relationships and reminding people about their products.

This presentation was a paperweight with a working dial, just like the ones used on the telephones. It was given out by the Automatic Telephone Manufacturing Company, whose logo you can see on the side.

The dial rotated and was a great alternative to drumming fingernails on the desktop.

Public telephone novice user : Alf Sawkins

Alf Sawkins is a 56 year-old engineer who grew up in the centre of Birmingham. He married at the age of 23 and moved to the outskirts of the city, which is when he had his first telephone at home.

Telecommunications has altered his life and his work in a variety of ways since that first phone was installed.

He explains how he tried to use a phone for the first time with a group of friends to confirm a booking for his local football team, with disastrous results.

audio clip


Right from a very small age I've always been interested in sport, particularly football, and we had a local street football team that actually got into a league. (it was) the only way we got communicated as to where we were playing each week and who we were playing. We were allocated a park in a letter; when we got that letter we then had to make arrangements to confirm the booking of the park. Now I remember on one occasion a group of about twelve of us ran the full length of two streets to reach a telephone box so that we could make a phone call. We got into it and nobody had got any money to put in so we then did the trip back, got some money, put it in, or tried to put in, and it didn't work because it was blocked up.

Keypad tones : pushing the right buttons

Keypad tones

fun and games

Can you beat our games? Explode equipment to see what's inside, hear the changing sounds of telecommunications, see how telecommunications designs have changed over time or send an e-postacard.

what's on

The UK's first permanent gallery dedicated to the history of information and communication technologies opens in the new Information Age gallery at London’s Science Museum.

audio history

Take a trip down memory lane with extracts of the interviews which have been recorded as part of the Connected Earth oral history programme.

featured story

100 years of automatic switching!
In 1912 the GPO installed Britain's first automatic telephone exchange in Epsom.

Discover the early days of the telephone...