Sporting Index pick two horses in a race and predict what the distance between them will be when they cross the line.
If you think one horse will beat another then you can place a bet on this market and it doesn't matter where in the field they finish - you are simply having a bet on their performance relative to each other. The maximum distances for the purpose of a match bet is 12 lengths in a Flat race and 15 lengths in a National Hunt race.
In the 2004 Oaks, Sporting Index pitted Ouija Board against Sundrop in a match bet. They made Ouija Board favourite to finish ahead of Sundrop by between 0-1 lengths.
If you thought Ouija Board was a far classier filly you might have gone high on Ouija Board over Sundrop at 1 length for £5 per length.
In the end Sundrop trailed in 12 lengths behind Ouija Board. So, had you gone high on Ouija Board at 1 length, then your bet would have paid off to the tune of 11 times your stake: (12 - 1) x your stake =11 x £5 = £55. If, however, Sundrop had finished 5 lengths ahead, the same bet would have lost you 6 times your stake (5 lengths plus the 1 length you bought at): (-5 - 1) x your stake = -6 x £5 = -£30.
Note it does not matter where the horses finish in the context of the race: it is simply the distance between them that counts.