If the transaction price of EUR/USD is 1.2400/03 and you buy EUR at 1.2403, then you are at “Long: EUR” or “Short: USD”. In another transaction, you decide to sell JPY. If USD/JPY transaction price is at 107.20/23, then you are at long USD and short JPY. Suppose that EUR rises to 1.2537 but JPY falls to 106.76, how will you do? Your profit and loss is like this. In EUR transaction, you bug 100,000 units of EUR at 1.2403 and sell them at 1.2537. Your profit is 0.0134 or $1.340 (.0134×Euro100,000=$1,340). In USD/JPY transaction, you bug $100,000 at 107.23 and sell them at 106.76. Your loss is 0.47 or $440.24 ($100,000×0.47=JPY47,000/106.76=$440.24). Your net profit is $899.76 ($1340 - $440.24=$899.76).