Why are some Minimum Probable Payoffs based on a $1 base wager amount and others based on a $2 base wager amount?

Base wager amounts vary from track to track for the reported Probable Payoffs of Exacta, Daily Double, and Quinella wagers. Some tracks use a $1 base wager amount when reporting their Probable Payoffs and other tracks use a $2 base wager amount. For this reason, it is important to pay attention to the displayed base wager amount when defining your minimum Probable Payoff.