Dear friends here : I would like to know how to write a formula to trigger a signal ONLY when one oscillating type indicator rise back from its oversell zone when it cross a trigger value at the first time . I use the RSI(14) as example . If I define the oversell zone is 30 and the trigger value at 45 . example : Value of RSI Day1- 48 Day2- 29 ( entered the oversell zone ) Day3- 25 Day4- 35 ( it left the oversell zone but not yet the trigger value ) Day5- 42 Day6- 47 ( it cross the trigger value 45 , I want this signal valid only , not any after UNTIL it drop under 30 again ) Day7- 50 Day8- 40 ( it drop under the trigger line again ) Day9- 48 ( it cross 45 again but this is what I want to filter out as it is not the first time it cross the trigger value after it entered the oversell zone , there maybe several times it drop under 45 and then cross over again . I want to filter all out until it drop under 30 and make another new valid signal ) I read the formula wrote by someone about the “shark ” formula in TASC but it seems hard to replace the function . I would like to have your help to do it in a flexible way and easy to replace the RSI when some other indicator are used .

thanks , smg . I will take a more detail look to it . Moreover . I would like to make this signal an alert signal only . The real trigger signal , eg , maybe a cross over a sma line so a cross over the 45 trigger line will only fullfill only a part of the entry requirement . Something like that .

Yes the latch takes four arguments, but you only need two, so replace the last with zeroes. Try this: ind:=RSI(C,14); LE:=ind>45; LX:=ind<30; SE:=0; SX:=0; extfml("Forum.latch",LE,LX,SE,SX); All you have to do now is to trap when the latch changes values to signal, which is in the manual. wabbit :D