# What P&L netting should one use when a strategy has trades in two different geographic locations?

Sell 1 for 10$Buy 2 for 10$
Sell 3 for 7$ and B.trades: Buy 1 for 5$
Buy 2 for 5$ If I concatenate B.trades to A.trades and run a fifo algorithm I get a realized PNL of 1$ with 1 share left long. However, if interleave them I could have:

Sell 1 for 10$Buy 1 for 5$
Buy  2 for 5$Buy 2 for 10$
Sell 3 for 7$ And then in that case the FIFO algorithm gives me a realized P&L of 6$ with one share long in the end. I can see from running this by hand that the reason is that the "more expensive" buy is left unmatched in the second case. But it illustrates how strongly it can influence P&L. Now, it's not always straightforward to interleave trades in correct order of time if the units are small and there is clock drift (measuring time in two different places with different clocks) so it's not always clear we can capture a universal ordering. What could be done or is done in practice with a situation like this?