In horse racing, collateral form refers to using the performance of horses against common opponents to compare their abilities.

For example, if Horse A and Horse B both raced against Horse C on different occasions, you can use their performances against Horse C to assess how they might perform against each other in a future race.

To use collateral form, you would need to look at the past races of the horses you are interested in and identify any common opponents they have faced. You would then compare their performances against those opponents to determine which horse has the better ability.

However, it’s important to keep in mind that collateral form is just one factor to consider when handicapping a race. Other factors like the horse’s recent form, the jockey’s performance, and the track condition should also be taken into account.