I was looking through the exchange traded spreads for financials and while I think I understand the calculation used Im not sure I understand the logic..... Why are they calculated from the previous days settlement and not a more convential calculation? If it is just the difference in the change between the 2 contracts for that day, then with the contract ratio the tick value for each leg would be different as well..... Is there a reason for the way it is set up or have I just misunderstood something.....