The Odd Differential Index is a market sentiment indicator. This index is simply calculated by subtracting the daily or weekly odd-lot sales from the daily or weekly odd-lot purchases. High readings appear near market tops and minus readings near bottoms. Introduced by Wall Street Courier, the Odd -Lot Differential Index indicates the market sentiment of small investors who purchase less than 100 shares of a stock. These market participants are usually wrong about the direction of the market and this indicator is therefore considered to be a contrary opinion sentiment indicator.