Reading the numbers
A pair of eights can be dealt 6 ways and a pair of sevens 6 ways. Once both hands are out, the cards they share leave 36 possible pairings. Each row above stands for every pairing with the same suit pattern. The best case for 88 is 82.5%, the worst 81.1%: a shared suit takes away flush cards, and a suit held by both hands can split a flush.
Equity counts half of each tie, so it is the share of the pot 88 takes on average if the money goes in now. Compare it with the from the pot odds calculator. For a whole range on each side, use the range equity calculator.