If it was zero, that means none of it can be explained. It would be a very bad fit. Capital S, this is the standard deviation of the residuals, and it's another measure of how much these data points vary from this regression line. Now this column right over here is going to prove to be useful for answering the question at hand. This gives us the standard error of the coefficient, and the coefficient that we really care about, the statistic that we really care about, is the slope of the regression line, and this gives us the standard error for the slope of the regression line. You could view this as the estimate of the standard deviation of the sampling distribution of the slope of the regression line. Remember, we took a sample of 20 folks here, and we calculated a statistic which is the slope of the regression line.