OBL1线开始上拐

下面公式，如何表示OBL1线开始上拐？ 想选上OBL1线开始上拐的股票
{N1=20 N2=3 N3=5}
N1:=20 ;
N2:=3 ;
N3:=5;
OBVN:=SUM(IF(CLOSE>REF(CLOSE,1),VOL,IF(CLOSE<REF(CLOSE,1),-VOL,0)),0);
MID:=MA(OBVN,N1);
UPPER:=MID+2*STD(OBVN,N1);
LOWER:=MID-2*STD(OBVN,N1);
OBL1:=(OBVN-LOWER)/(UPPER-LOWER)*100,COLORGRAY;
OBL2:=EMA(OBL1,N2),COLORRED;
OBL3:=EMA(OBL2,N3),COLOR00DDDD;