What it says in the resources (click on "margining") doesn't make much sense to me. It says that
"We employ a proprietary algorithm to estimate the current Forward premium or discount. This algorithm draws data from various markets that offer to trade instruments on the future delivery of bitcoin."
However, to estimate the premium, wouldn't you have to look at bitcoin spot price rather than other derivative exchanges? I think it probably means "from various spot markets".
They use the premium to calculate the margin you have, or the level of collateral you need to have posted. It is different from the bitcoin price, to avoid sell-offs, as in self feeding flash crashes. Anyway it is not needed for your own calculations of profit or loss, so you can largely ignore it. Just look at the price and make up your mind on what it will be weeks or months from now.