How to arrows unchanged?

Code Behgozin slope finder:
SetChartBkGradientFill(1,23);
_SECTION_BEGIN("Behgozin Slope Finder");

Tr2 = Ref(C,1);
Tr3=Ref(C,7);
Trend2 = MA(Tr2,7);
Trend3=MA(Tr3,7);
Slope1=((Trend3-Trend2)/Trend3)*100;
Plot(Slope1,"Buy When it is Green and Sell when it is Red or Pink",colorGold,styleLine+styleDots|styleThick);


Tr4 = Ref(C,7);
Tr5=Ref(C,15);
Trend3 = MA(Tr4,15);
Trend4=MA(Tr5,15);
Slope2=((Trend4-Trend3)/Trend4)*100;
Plot(Slope2,"",colorGreen,styleLine+styleDots|styleThick);
Plot(0,"",colorWhite,styleLine);
_SECTION_END();SetSortColumns(-2);

//Richu


Buy= nwbull=slope1 > 0 AND slope2 > 0 ;
Sell=nwbear=slope1 < 0 AND slope2 < 0 ;
Buy = ExRem( Buy, Sell );
Sell = ExRem( Sell, Buy );

PlotShapes(IIf(Buy,shapeUpArrow,Null),colorGreen,0,0,-10);

PlotShapes(IIf(Sell,shapeDownArrow,Null),colorRed,0,0,-10);

Plot( 1, /*efines the height of the ribbon in percent of pane width */"ribbon",
IIf( nwbull, colorLime, IIf( nwbear, colorRed,IIf(Signal()<MACD(), colorPink, colorPink ))), /* choose color */
styleOwnScale|styleArea|styleNoLabel, -01, 50 );
however, the signal to buy, resell change over realtime so inaccurate. How to make arrows unchanged (non-repaint). thank all the ah.