I don't understand this.

[Methworathanung Thanessagon]

I don't understand this. Can someone explain this to me.

[William Roeder]

You buy at the Ask and sell at the Bid. Pending Buy Stop orders become market orders when hit and open at the Ask.

1. Your buy order's TP/SL (or Sell Stop's/Sell Limit's entry) are triggered when the Bid / OrderClosePrice reaches it. Using the Ask±n, makes your SL shorter and your TP longer, by the spread. Don't you want the specified amount used in either direction?

2. Your sell order's TP/SL (or Buy Stop's/Buy Limit's entry) will be triggered when the Ask / OrderClosePrice reaches it. To trigger close to a specific Bid price, add the average spread.
             MODE_SPREAD (Paul) - MQL4 programming forum - Page 3 #25

3. The charts show Bid prices only. Turn on the Ask line to see how big the spread is (Tools → Options (control+O) → charts → Show ask line.)
   Most brokers with variable spreads widen considerably at end of day (5 PM ET) ± 30 minutes. My GBPJPY (OANDA) shows average spread = 26 points, but average maximum spread = 134 (your broker will be similar).