The middle line can be configured with the parameter Middle line type as:
MID_TYPE_NONE=0, // None
MID_TYPE_MEDIAN=1, // Median, (high + low)/2
MID_TYPE_TYPICAL=2, // Typical, (high + low + close)/3
MID_TYPE_WEIGHTED=3 // Average, (high + low + close + close)/4
MID_TYPE_MEDIAN=1, // Median, (high + low)/2
MID_TYPE_TYPICAL=2, // Typical, (high + low + close)/3
MID_TYPE_WEIGHTED=3 // Average, (high + low + close + close)/4
