What is the purpose of the "Betting Value" column in the exacta wagers?

This column indicates whether an individual exacta combination is an overlay (positive) or underlay (negative) according to a formula that calculates the fair value return based on the current win odds.

In general, a betting value above 100% indicates an overlay. A negative Betting Value means that particular combination is being played heavily by other horseplayers; you may want to delete that specific combination.