The stop loss calculation index of MT4 platform is ATR index. ATR(Average True Range) is the average true volatility index, which is calculated according to the highest price, lowest price and yesterday's closing price. In MT4 platform, the method of calculating stop loss with ATR index is as follows:

Select the currency pair to be traded in the chart, right-click the pop-up menu, and select Indicator-Trend-Average Real Range (ATR) in the navigation menu.

The ATR setting window pops up, where you can select the number of days for calculating ATR indicators, line color, line width and other parameters.

Drag the mouse in the chart, select the appropriate stop loss point, click the right mouse button at the stop loss point, and select "Transaction"-"New Order" in the pop-up menu.

In the new order window, select the "Stop Loss" option, and fill in the stop loss price calculated by ATR indicator in the "Stop Loss Price" input box to confirm the order.

It should be noted that the stop-loss price calculated by ATR index is based on the historical fluctuation range and cannot fully represent the future fluctuation. Investors need to make careful decisions when using stop loss.