Chuck Lebeau in his Traders Club Bulletin N. 47 describes the ATR Ratchet Stop (http://traderclub.com/discus/messages/107/1501.html?SaturdayJuly2120010131pm).
He gives the following description of the logic:
"Here is an example of the strategy: After the trade has reached a profit target of at least one ATR or more, we pick a recent low point (such as the lowest low of the last ten days). Then we add some small daily unit of ATR (0.05 ATR for example) to that low point for each day in the trade. If we have been in the trade for 15 days we would multiply 0.05 ATRs by 15 days and add the resulting 0.75 ATRs to the starting point. After 20 days in the trade we would now be adding 1.0 ATRs (.05 times 20) to the lowest low of the last ten days."
He suggests waiting to use the exit until some minimum level of profitability has been reached because this stop has a way of moving up very rapidly under favorable market conditions.
"One of the nice features about the ATR Ratchet is that we can start it any place we want. For example we can start it at some significant low point just as the Parabolic does. Or we can start it at a swing low, a support level, and a channel low or at our entry point minus some ATR unit. If we wait until the trade is fairly profitable we could start it at the entry point or even somewhere above our entry point."
This represents a first attemp at writing the ATR Ratchet.

Buy:= Cross(Mov(C,10,E),Mov(C,20,E)) ;
Sell:= Cross(Mov(C,20,E),Mov(C,10,E)) ;
I:=Cum(Buy + Sell > -1) = 1;
Tr:=If(BarsSince(Buy OR I) < BarsSince(Sell OR I),1,-1);

acc:=Input("Acceleration Factor in Percent",.01,.10,.02);
brs:=Input("Lookback periods",1,100,10);
acf1:=(acc)*BarsSince(Buy);
acf2:=(acc)*BarsSince(Sell);
val1:=LLV(L,brs)+acf1*ATR(14);
val2:=HHV(H,brs)-acf2*ATR(14);
rat:=If(Tr=1,val1,val2);
rat;

Any suggestions on improving the above formula would be appreciated.
Thank and regards.

Maurizio