Sky, BBC and ITV all have their own versions - which have proven to be very accurate.
The nation was stunned - as was PM May, in 2017 - with a high number of lost seats predicted for the Conservatives.
Less than half a minute after the polls closed - and hotly disputed by many. But later proved to be uncannily accurate.
Polling modus operandi is simple. Pollsters attend about 140 polling stations, and approach 180 voters (thereabouts) - usually around every 15th, or so; this is to avoid groups of similar voters.
The individual is asked to mark his/her decisions on a mock voting paper, and to insert it in a designated box; these boxes are collected during the day.
As history has shown, for example, that Labour voters visit polling stations later than Conservative ones. The last boxes are collected 20 minutes before the polls close.
Thus 25,000+ voters have been involved - and past exit polls have confirmed that voters, almost always, provide accurate data.
UK is one of the most accurate countries for exit polls - helped by its first past the post voting system. PR makes things a lot more difficult for pollsters.
So - soon after 10pm, this coming Thursday - the nation will probably know its future. And be able to contemplate it in bed - instead of having to watch TV all night.