Swingometer

The swingometer is a graphics device that shows the effects of the swing from one party to another on British election results programmes. It is used to estimate the number of seats that will be won by different parties, given a particular national swing (in percentage points) in the vote towards or away from a given party, and assuming that that percentage change in the vote will apply in each constituency. The device was invented by Peter Milne, and later refined by David Butler and Robert McKenzie.

The first outing on British television was during a regional output from the BBC studios in Bristol during the 1955 general election (the first UK general election to be televised) and was used to show the swing in the two constituencies of Southampton Itchen and Southampton Test.

Following this use in 1955, the BBC adopted the swingometer on a national basis and it was unveiled in the national broadcasts for the 1959 general election. This swingometer merely showed the national swing in Britain but not the implications on that swing on the composition of parliament. These issues were not addressed until the 1964 general election.

The swingometer for that election showed not only the national swing, but also the implications of that national swing. So for instance, a 3.5% swing to Labour would see Labour become a majority government whilst any swing to the Conservatives would see Sir Alec Douglas-Home reelected as Prime Minister with a huge parliamentary majority. In the end the result was a Labour overall majority of 4, and so when the 1966 general election came around, a new element had to be added (namely the prospect of a hung parliament).

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