Calculation of Volume Weighted Effective Spread if one of the trades had negative E.S ?

CFA Level III
#1

Here are the two transactions for purchase of Stock Mid Quote Actual Price Volume

12.05 12.10 1000

12.08 12.07 500 As seen in transaction 2 we were able to purchase the stock at a price less than the mid quote. I believe that we will still consider the absolute value (and not the negative value for 2nd trade) as E.S accounts for a two- way trade, and if we bought at a lower price, it means somebody must have sold for a lower price too. Can somebody please confirm.

#2

I think effective spread would be negative for trade 2.

so the weighted for 2 is .03.