sorry, mine badly written. there is actually 2 legs of trades.
below is just an example on ICE Brent
On 1st Mar
Sold Apr @ 118.15
Bought May @ 117.25
On 15th Mar
Bought Apr @ 109.47
Sold May @ 109.34
For Apr, the gain is 8.68
For May, loss is -7.91
now the diff is 0.77, n that...