A short-term technical indicator (simply known as Arms index or TRIN) that measures the strength of the volume of advancing stocks relative to the strength of declining stocks. It is calculated as:

An index reading of more than one means more activity in declining stocks, whilst a reading of less than one indicates more activity in advancing stocks.

This index (named after its inventor Richard Arms) is a contrary indicator that trends in the opposite direction of the market. However, a 10-day moving average of this index is a workable way to better grasp its contrary nature.