This section introduces the OLS formula, the formula we use to find a straight trend line through a scatter plot. In this section, the formula is presented without any derivation. We will also look at how to find trendlines in EViews, Stata and Excel. Once we have our scatter plot and trendline, we can define residuals and fitted values. Using the residuals, we can introduce the least squares principle, the principle behind the OLS formula. Finally, we look at the special case when the intercept of our trend line is zero ("no intercept").