The Mass Index is an indicator that was developed by Donald Dorsey and is primarily used to predict market reversals. It measures a range of high to low prices for a specific period of time. The mass index helps indicate when a reversal may take place when the range widens past a certain point and then contracts, this area is called the bulge. When the Mass index gets above 27, and then drops below 26.5, that is an indication of a reversal.

A trader can set a baseline below 27 if it is a less volatile stock.

Calculation:

Take the 9-period EMA over and an exponential moving average of this average. Then sum the ratio of the two over a given number of days, usually 25

Mass = Sum[ 25 ] of  EMA[ 9 ] of ( high - low )  /  EMA[ 9 ] of EMA[ 9 ] of ( high - low )