On-balance volume
Volume is a very important variable in investing; it indicates how big a price move is. The on-balance volume indicator is one of the simplest stock price indicators. It is based on the close price of the current and previous days and the volume of the current day. For each day, if the close price today is higher than the close price of yesterday then the value of the on-balance volume is equal to the volume of today. On the other hand, if today's close price is lower than yesterday's close price then the value of the on-balance volume indicator is the difference between the on-balance volume and the volume of today. If the close price did not change then the value of the on-balance volume is zero.