This indicator was originally developed by Curtis McKallip Jr. (Stocks & Commodities, V.10:7 (296-299): "The Damping Index").
It indentifies bars where the highs and lows are getting close and closer. A high Damping Index value means that the difference between the high price and low price is becoming lower and the security price is reaching equilibrium. A low Damping Index value means that the difference between the high and low prices is increasing.