Each brokerage companies has its own GMT offset (the difference in hours between GMT +0). We use the MetaTrader 4 terminal provided from them and we should comply with their GMT offsets. Many forex robots are GMT dependant. They need correct GMT offset to trade properly and show good results.
Due to its trading strategy Forex Diamond EA doesn't require GMT offset to be set in the robot settings for live trading. But it needs for backtesting! Therefore we will explain in details how to set correct GMT offset in Forex Diamond EA settings.