How is "profitability" calculated? it doesn't make any sense to me.  Some examples from the ASIC tab today using 0.075 $ power:

Bitcoin: Revenue is showing as $6.46, profit is showing $3.74 and the profitability is showing as 100%.  There isn't any math I can figure where profitability is 100%.
Siacoin: Revenue showing 3.93 and profit is 1.59 and profitability is 60%.  

The way I would normally look at profit margin or profit ratio would be profit over power so in the case of bitcoin it would be $3.74/($6.46-3.74)= 1.37 so a 1.37 or 137% profit ratio of net revenue over power.  I have no clue where the 100% comes from.

Can someone help explain or point to a formula that explains the profitability calculation on the site?