為何提示不允許是-1

?死叉:=CROSS(DEA,DIF);
N1:=BARSLAST(死叉),NODRAW;
N2:=REF(BARSLAST(死叉),N1+1),NODRAW;
N3:=REF(BARSLAST(死叉),N2+N1+2),NODRAW;
CL1:=LLV(C,N1+1),NODRAW;
DIFL1:=LLV(DIF,N1+1),NODRAW;

CL2:=REF(CL1,N1+1),NODRAW;
DIFL2:=REF(DIFL1,N1+1),NODRAW;
CL3:=REF(CL2,N1+1),NODRAW;
DIFL3:=REF(DIFL2,N1+1),NODRAW;
PDIFL2:=IF(DIFL2>0,INTPART(LOG(DIFL2))-1,INTPART(LOG(-DIFL2))-1);

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老師上面公式為何軟件提示如下：

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第16行 'IFL2'面不允許是'1'

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?來源:程序化99