代码是：

Params

   Numeric FastLength(12);

   Numeric SlowLength(26);

   Numeric MACDLength(9);

Vars

   Numeric MACDDiff;

   Numeric AvgMACD;

   Numeric MACDValue;

Events

   OnReady()

   {  

   }

   OnBar(ArrayRef<Integer> indexs)

   {

   Range[0:DataCount-1]  {

MACDDiff = XAverage( Close, FastLength ) - XAverage( Close, SlowLength ) ;    

AvgMACD = XAverage(MACDDiff,MACDLength);

MACDValue = MACDDiff - AvgMACD;  

}

print(Text(MACDValue));

print(Text(data1.MACDValue));

                       print(Text(data2.MACDValue));

                       print(Text(data1.MACDValue[1]));

}

报错：

请问官方大佬，我想回溯前N根bar的MACDValue，要怎么获得呢？  不管是前一根或者前10根的值都行。