int OnCalculate(
   const int rates_total,       // 全部で何本の足があるか
   const int prev_calculated,   // 前回まで計算済みの本数
   const datetime &time[],
   const double &open[], const double &high[],
   const double &low[],  const double &close[],
   const long &tick_volume[], const long &volume[],
   const int &spread[]
);

double MyBuffer[];

#property indicator_chart_window
#property indicator_buffers 1

int OnInit()
{
   SetIndexBuffer(0, MyBuffer);
   return(INIT_SUCCEEDED);
}

int OnCalculate(const int rates_total, const int prev_calculated,
                const datetime &time[], const double &open[],
                const double &high[], const double &low[],
                const double &close[], const long &tick_volume[],
                const long &volume[], const int &spread[])
{
   int start = (prev_calculated > 0) ? prev_calculated - 1 : 0;
   for(int i = start; i < rates_total; i++)
      MyBuffer[i] = (high[i] + low[i]) / 2;
   return(rates_total);
}