The Open-10 TRIN function is a market breadth indicator that uses advancing/declining volume and advancing/declining issues to measure market strength.

The Open-10 TRIN is similar to the Arms Index, Advancing/Declining Ratio, and the Upside/Downside Ratio in that it makes a good overbought/oversold indicator. Extremely low values may indicate that the market is becoming overbought and a sell-off should occur in the near future resulting in lowered prices. Likewise, extremely high values can indicate an oversold market. Readings >0.90 are considered bearish and readings <0.90 are considered bullish.

The Open-10 TRIN keeps running totals of advancing and declining volume as well as advancing and declining issues for the last ten days. It is calculated by dividing the number of advancing issues by the number of declining issues and the amount of advancing volume by the amount of declining volume. The ratio of advancing to declining issues is then divided by the ratio of advancing to declining volume.

Note that the running totals are effectively the same as taking a moving average of each parameter since the division by the length of each average cancels out.