A standard market order contains two stop orders - StopLoss and TakeProfit. They instruct to close the order at the requested prices in order to stop losses and fix profits. Modification of market orders may be useful for changing of the requested prices of stop orders either as a result of new calculated values obtained in the program or at the trader's initiative. The client terminal has its own tool used for modification of StopLoss: Trailing Stop. It allows the program to modify the level of StopLoss following the rate at a certain fixed distance from it (see MetaTrader 4 Cleitn Terminal User Guide).