Horse tracking app for the Grand National (channel4.com)

Used this during the race and it was damn impressive, think it dropped out about 3 times. I would say 95% of the race it was accurate.

But I can't get my head around how it was all done.

As soon as my horse fell, the app said DNF.

I presume it's a mix of internet data (horses carry tracking devices or pass markers and have tags on them) and also signals from the TV.

Any better explanation appreciated.

Dave