[amibroker] Drawing Stop Loss Line

[rpc20060610]

Hi 
I want to draw a Stop Loss line (Horizontal)  at 5 % below the the 
lower of current bar(where Buy is triggered) or earlier bar whichever 
is lower.I am finding difficult to determine how to find where did last 
buy occur on the chart from within the AFL.
Any help in this regard will be greatly appreciated
rpc20060610