Darvas Box 

Here is my version for both buy and sell 

LL:=If(L=LLV(L,5),L,If(Ref(L,-1)=LLV(L,5),Ref(L,-1),If(Ref(L,-2)=LLV(L,5),Ref(L,-2),If(Ref(L,-3)=LLV(L,5),Ref(L,-3),If(Ref(L,-4)=LLV(L,5),Ref(L,-4),0))))); 
HH:=If(H=HHV(H,5),H,If(Ref(H,-1)=HHV(H,5),Ref(H,-1),If(Ref(H,-2)=HHV(H,5),Ref(H,-2),If(Ref(H,-3)=HHV(H,5),Ref(H,-3),If(Ref(H,-4)=HHV(H,5),Ref(H,-4),0))))); 
NH:=ValueWhen(1,H>Ref(HHV(H,5),-1),H); 
NL:=ValueWhen(1,L<Ref(LLV(L,5),-1),L); 
Set1:=HHV(H,3)<HHV(H,4); 
Set2:=LLV(L,3)>LLV(L,4); 
Val1:=ValueWhen(1,BarsSince(H>Ref(HHV(H,5),-1))=3 AND Set1=true,NH); 
Val2:=ValueWhen(1,BarsSince(L<Ref(LLV(L,5),-1))=3 AND Set2=true,NL); 
Val3:=ValueWhen(1,BarsSince(H>Ref(HHV(H,5),-1))=3 AND Set1=true,LL); 
Val4:=ValueWhen(1,BarsSince(L<Ref(LLV(L,5),-1))=3 AND Set2=true,HH); 
Per1:=Input("max length",10,100,30); 
RWH:=(H-Ref(L,-Per1))/(ATR(Per1)*Sqrt(Per1)); 
RWL:=(Ref(H,-Per1)-L)/(ATR(Per1)*Sqrt(Per1)); 
Pk:=Mov((RWH-RWL),3,W); 
TB:=If(Pk>0,Val1,Val4); 
BB:=If(Pk>0,Val3,Val2); 
TB;BB; 

Here is the original version for long 

LL:=If(L=LLV(L,5),L,If(Ref(L,-1)=LLV(L,5),Ref(L,-1),If(Ref(L,-2)=LLV(L,5),Ref(L,-2),If(Ref(L,-3)=LLV(L,5),Ref(L,-3),If(Ref(L,-4)=LLV(L,5),Ref(L,-4),0))))); 

NH:=ValueWhen(1,H>Ref(HHV(H,5),-1),H); 

Set1:=HHV(H,3)<HHV(H,4); 

Val1:=ValueWhen(1,BarsSince(H>Ref(HHV(H,5),-1))=3 AND Set1=true,NH); 

Val2:=ValueWhen(1,BarsSince(H>Ref(HHV(H,5),-1))=3 AND Set1=true,LL); 


TB:=Val1; 
BB:=Val2; 
TB;BB;