The TRIN, or Arms index, developed by Richard Arms in the 1970s, is a short-term technical analysis stock market trading indicator based on the Advance-Decline Data.
The index was introduced by Richard Arms, and is continuously displayed during trading hours, among other indices, on the New York Stock Exchange's central wall display for the stocks traded on that exchange.
The denominator of the index is calculated based on number of shares traded, not their dollar value.
The Arms Index, also known as the TRIN, is part of the galaxy of technical indicators used to measure and predict the movements of the stock market.
As with other technical indicators, it is most effective when combined with other analytical tools.