Currency futures

Hi John,

Firstly, thank you for the lectures, they have helped massively and without them, I’m sure I’d have not come this far in my studies.

On to my question;
When estimating the futures or spot rate using basis, do we always use the mid market rate for the spot? I’m working on example 11 in chapter 18, whereby I’ve used 1.4821 instead of the average between the two rates. And then again used the left hand rate on the date of the transaction. This of course gives a different futures rate at the transaction date and then a different gain when evaluating the hedge. So again, when estimating, is it only the mid market rate that can be used to calculate the basis?

Thanks in advance.