Mass Index

The Mass Index sums the ratio of a 9-period EMA of the high-low range to a double 9-period EMA of that range over a 25-bar window, producing an oscillator that rises as the trading range widens relative to its own smoothed baseline. It carries no directional information at all — the design detects range expansion and contraction, and its traditional read is the reversal bulge: a climb above 27 followed by a drop back below 26.5. Defaults match Donald Dorsey's original specification, and the script plots the Mass Index line against two dashed reference levels, the Setup Level and the Trigger Level.

How to Trade the Mass Index?

• Cross above the Setup Level (27): ranges have expanded well beyond their smoothed baseline — the bulge is armed.
• Subsequent drop below the Trigger Level (26.5): the contraction that completes the reversal bulge, traditionally read as raised odds that the prevailing move is exhausting.
• Rising index without a bulge: general range expansion; falling readings mark quieting bars.
• Direction comes from elsewhere: the index says a turn is more likely, never which way — a trend read such as the slope of a short moving average supplies the side.

Mass Index Settings

• Sum Length (default 25): bars over which the single/double EMA ratio is summed — longer smooths the index and makes bulges rarer; shorter shifts its typical level lower.
• EMA Length (default 9): length of the single EMA of the high-low range and of its double smoothing.
• Setup Level (default 27): the arm level for the reversal bulge.
• Trigger Level (default 26.5): the completion level; widening its gap below the Setup Level delays triggers.

Frequently Asked Questions

What exactly is the reversal bulge?

A two-step pattern in this build's pane: the index crosses up through the Setup Level as bar ranges widen dramatically, then falls back through the Trigger Level as they contract. That round trip flags volatility structure consistent with exhaustion of the move in force, in either direction.

Do the 27 and 26.5 levels work everywhere?

They are conventions tied to the default 25-bar sum, where the index oscillates around the mid 20s. Change the Sum Length and the whole scale shifts, which is why the levels are exposed as inputs rather than hard-coded — calibrate them to the instrument's observed range if bulges never fire or fire constantly.

What alerts does this build include?

Both halves of the pattern are covered: a Bulge Setup alert fires when the Mass Index crosses above the Setup Level, and a Bulge Trigger alert fires when it drops back below the Trigger Level, so the two-step sequence can be tracked without watching the pane bar by bar.