In academic literature it is more common to base analysis on stock returns and log returns of the close price. Simple returns are just the rate of change from one value to the next. Logarithmic returns or log returns are determined by taking the log of all the prices and calculating the differences between them. In high school, we learned that the difference between the log of "a" and the log of "b" is equal to the log of "a divided by b". Log returns, therefore, also measure rate of change. Returns are dimensionless, since, in the act of dividing, we divide dollar by dollar (or some other currency). Anyway, investors are most likely to be interested in the variance or standard deviation of the returns, as this represents risk.