Spread = cost.
You need to pay for every trade(in and out) that you make.
If you code it “into the stop loss” then ur not seeing that cost on every trade that does not hit stop loss.
lets say you take a trade and it hits target. if you have your “spread” coded into your stop loss then that trade would be free, when in fact in real life that trade would have cost u the spread for in and out.
