Trailing stop order - In this order type, the stop price follows the market at a fixed distance (known as the Trail Amount) when the market is moving in favour of the trader. However, stop price remains unchanged when the market is moving against the trader. This feature of trailing stop orders enables a trader to specify a limit on the maximum possible loss, without setting a limit on the maximum possible gain. When the market reaches the trigger price, a market order is sent to the other book.
For this order, the Trigger Price will follow the Triggering Index at a distance of 40 when the Triggering Index Price is going down. And, a Buy market order of 50 contracts will be sent to the order book when Triggering Index Price rises by 40.