Calculating back values

#property indicator_separate_window
#property indicator_buffers 2
#property indicator_color1 Blue
#property indicator_color2 Red
//---- input parameters
extern int       bbPeriod    =          20;
extern int       bbDeviation =           2;
extern int       bbPrice     =           0;
extern int       bbDigits    =           2;
int       lookback    =         120;
double Bandwidth[],BWMin[];
//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int init()
  {
   IndicatorBuffers(4);
   IndicatorShortName("Bandwidth - Period="+bbPeriod+"    ");   
   SetIndexStyle(0,DRAW_LINE);
   SetIndexBuffer(0,Bandwidth);
   SetIndexLabel(0,"Bandwidth");
   SetIndexStyle(1,DRAW_LINE);
   SetIndexBuffer(1,BWMin);
   SetIndexLabel(1,"BWMin");
   IndicatorDigits(Digits+1);
   return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator deinitialization function                       |
//+------------------------------------------------------------------+
int deinit()
  {
//----
 
//----
   return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
int start()
  {
   //Bar stuff
   int    counted_bars=IndicatorCounted();
   int limit, shift, shift2; 
   double bbUpper, bbLower, bbMiddle;
   if(counted_bars<0) return(-1); 
   limit=Bars-counted_bars-1;
 
   for(shift=0; shift<limit; shift++)
      {
      bbUpper=iBands(NULL,0,bbPeriod,bbDeviation,0,bbPrice,MODE_UPPER,shift);
      bbLower=iBands(NULL,0,bbPeriod,bbDeviation,0,bbPrice,MODE_LOWER,shift);
      bbMiddle=iBands(NULL,0,bbPeriod,bbDeviation,0,bbPrice,0,shift);
      Bandwidth[shift]=NormalizeDouble(((bbUpper-bbLower)/bbMiddle)*100,bbDigits); 
      }
 
   for(shift2=0; shift2<limit; shift2++)
      {  
      double MinBw=Bandwidth[ArrayMinimum(Bandwidth,lookback,shift2+1)];
      BWMin[shift2]=(MinBw*0.25)+MinBw;
      }
 
   return(0);
  }