I tried using iLowest ((iLowest(NULL,PERIOD_M15,MODE_LOW,3,1)) but when tested in MT4 it wont modify the SL at correct price, even in other trade SL was not modified at all.
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As written in the reference (F1 if the cursor is above it) iLowest() returns the index of the bar with the lowest 'what-ever' (may that's why it begins with iLowest()?) - not the value.
Just see the example there!