Source: https://fxcodebase.com/code/viewtopic.php?f=17&t=900
Forum: 17 · Topic 900 · 3 post(s)
Alexander.Gettinger · Fri Apr 30, 2010 12:28 pm
The mass index serves for finding turns in trends. It is based on changes between maximum and minimum prices. If the amplitude gets wider, the mass index grows; if it gets narrower, the index gets smaller.
Calculation:
MI = SUM (EMA (HIGH - LOW, 9) / EMA (EMA (HIGH - LOW, 9), 9), N)
Where: SUM — means a sum; HIGH — the maximum price of the current bar; LOW — the minimum price of the current bar; EMA — the exponential moving average; N — the period of the indicator (the number of values added).

The indicator was revised and updated
Alexander.Gettinger · Thu Apr 03, 2014 10:57 am
MQL4 version of Mass Index: viewtopic.php?f=38&t=60489.
Apprentice · Fri Jun 16, 2017 7:23 am
The indicator was revised and updated.