When we say about an object relative to something, this only means that we are comparing an object’s characteristic to that of our reference. So in this case, I think we are referencing Delia’s jump to someone else. Say our reference has a long jump length of 5 meters, since Delia’s relative long jump length is 0, this means that relative to the reference there is no difference. Therefore, Delia’s jump length is also 5 meters.