Hi, If i want to buy every time the close price goes up 10%, then close out, and then sell short every time the close drops 10%. How should I code. E.g. C1=8, C2=9 (buy) C3=10(buy) Then sell at C4 Then when C5=10 C6=8 (Sell short) C10=6(Sell short) C12=4 (Sell short) My buy/sell short conditon is based on the previous buy/sell short price. I have asked similar questions about it before. First of all, Thank you for replying. I saw some people have this kind of backward reference questions as well, and GV.dll or latch or prev/valuewhen are advised. But I am still not quite understand how to use GV.dll and latch. I have work out the formula for buy conditon, and it is fine to me: var1:=valuewhen(1,C*0.9>prev, C); var2:=valuewhen(2,C*0.9>prev, C); Cross(var1,var2*1.1) But, when I use the similar idea in sell short. It doesnt work. I am still new to MS, so if you have a better solution for this, please help me with this. Thanks.