This indicator is inspired from the mass index indicator with the goal of telling the user when a trend is about to stop thus highlighting potential reversals.
When the indicator cross under the trigger line the trend is about to stop and may reverse, shorter length will spot shorter terms reversals but a length of 100 is a good value.
This indicator was originally developed by Donald Dorsey (Stocks & Commodities, V.10:6 (June, 1992): "The Mass Index").
Specially for @AlexMayorov :
If indicator reaches 27 and then falls to below 26.5 then it could be a signal of potential trend reversal.