Unlike the other most prestigious steeplechase of the year, the Cheltenham Gold Cup, the Grand National is a handicap race.

This means that horses carry differing weights according to their previous form.

The idea behind a handicap is to make for a more even race - the handicapper's ultimate (though in practice unfeasible) aim is for the horses to pass the winning post in a dead heat.

The "best" horse in the race is given the top weight (usually 12 stone) and the weights allotted to the other horses are set in relation to this.

This means that if the top-weighted horse drops out, the weights of the other competitors may alter but will not change in relation to each other.

The weights for the Grand National are set two months before the race.

Horses can also run in other races in between the handicap being set and the race being run.

Seasoned punters will look out for these runs as these give a chance to spot horses whose talent may not have been accurately reflected by the handicapper.

For example, when the handicapper allots a weight to a horse for the Grand National, he will look at its previous form.

But if a horse had been run over the wrong distance or had simply run below par on a given day, that would not be a true indication of how good it was.

It may then run at a more suitable distance and perform much better after the handicap had been set but before the Grand National itself.

The horse would then be said to be carrying a favourable weight in comparison to its Grand National rivals.

There are exceptions - some valuable races automatically carry weight penalties so that would be added to a horse's Grand National weight because the horse would have been adjudged to have significantly improved to warrant this.

Minimum weight

Even if a horse is allotted a weight of 8 stone 12, it must carry 10 stone as this is the required minimum.

This means that some horses will be carrying possibly a stone more than they should be (known as being out of the handicap) and this disadvantage should suggest that they are likely to perform less well than their rivals.

Many punters will automatically put a line through horses out of the handicap although last year's winner Bobbyjo was a horse who performed above his handicap rating.

The Grand National is a test of endurance and it is noteworthy that no horse since Rhyme 'n' Reason back in 1988 has won carrying more than 11 stone.