One example takes place when the run-ups are variable, like when they changed them this meet at Belmont. Length of run-up affects the time of the race, and if your speed chart is based on ones that don't exist on a given day it will be wrong. Another example is track maintenance-- all parts of the track don't always get the same things done. Weather itself can also be a factor-- the stretch and backstretch at Belmont can be dramatically different, depending on wind and shade. And sometimes we don't know why things are different, but we know they are, by looking at how fast the horses run at different distances.



TGJB