I'm not an expert sports better... but I'll hazard a guess.

The numbers are arithmetic inverses of each other. So in odds terms you could use either the left or right numbers to determine payoffs. If you're laying 1.7 to 1 odds, for example, you'd get paid off at .59 per $1 you bet. On the other hand, if you're getting 1.7 to 1 odds, you'd get $1 for every .59 you bet.

Don't know if this is the case, but it kinda makes sense to me.