ZigZag indicator on MT4 version 4 build 1010; bug or am I stupid?

I have a newbie question about coding. As you see on below picture I attached 2 ZigZag indicator to a chart. First with parameter Deviation=1000 color white and second with Deviation=5 color red. As you see there is not influence of Deviation parameter (indicators are overlapped).

 I looked at the source code and saw these lines:

//--- main loop      
   for(i=limit; i>=0; i--)
     {
      //--- find lowest low in depth of bars
      extremum=low[iLowest(NULL,0,MODE_LOW,InpDepth,i)];
      //--- this lowest has been found previously
      if(extremum==lastlow)
         extremum=0.0;
      else 
        { 
         //--- new last low
         lastlow=extremum; 
         //--- discard extremum if current low is too high
         if(low[i]-extremum>InpDeviation*Point)
            extremum=0.0;
         else
           {
            //--- clear previous extremums in backstep bars
            for(back=1; back<=InpBackstep; back++)
              {
               pos=i+back;
               if(ExtLowBuffer[pos]!=0 && ExtLowBuffer[pos]>extremum)
                  ExtLowBuffer[pos]=0.0; 
              }
           }
        } 
      //--- found extremum is current low
      if(low[i]==extremum)
         ExtLowBuffer[i]=extremum;
      else
         ExtLowBuffer[i]=0.0;
      //--- find highest high in depth of bars
      extremum=high[iHighest(NULL,0,MODE_HIGH,InpDepth,i)];
      //--- this highest has been found previously
      if(extremum==lasthigh)
         extremum=0.0;
      else 
        {
         //--- new last high
         lasthigh=extremum;
         //--- discard extremum if current high is too low
         if(extremum-high[i]>InpDeviation*Point)
            extremum=0.0;
         else
           {
            //--- clear previous extremums in backstep bars
            for(back=1; back<=InpBackstep; back++)
              {
               pos=i+back;
               if(ExtHighBuffer[pos]!=0 && ExtHighBuffer[pos]<extremum)
                  ExtHighBuffer[pos]=0.0; 
              } 
           }
        }
      //--- found extremum is current high
      if(high[i]==extremum)
         ExtHighBuffer[i]=extremum;
      else
         ExtHighBuffer[i]=0.0;
     }

I do not understand why this parameter has no influence on the chart. Please basic explanation. I am newbie at coding/

Thanks in advance!

PS It is a built in indicator in MT4 software.