Sky sports racing percentages

[Bakersboy]

I am watching sky sports racing and, during races, the horse numbers appear at the bottom of the screen. But what do the percentages under each horse number mean?

[nolte]

I looked at the 7:35pm at ripon, it looks like an live probability rating of winning for each horse for the race

You can see it going to zero for the back markers as the end of the race and they drop back.

As horses move in the bunch there percentage changes