This is a scatter diagram of the five tallest buildings in Chicago, Y = Height in feet. Type in guesses for the intercept a and slope b, then press Enter or use the sliders on either side of the plot to adjust the line. As you change the line, notice the values in the table below.

• The first two columns give the X and Y values.
• The third column gives a + b × X, the point on the line associated with that X. On the graph, a red line segment is drawn from the Y value to that point on the line.
• The fourth column is the residual, Y - (a + b×X). Its absolute value is how far vertically the point is from the line: it is the length of the red line segment.
• The goal is to have a line with small residuals, that is, for which the red line segments are short. As you adjust the line, you see that some residuals become smaller and some larger.

Adjust your line so to have the smallest sum of the squared residuals, that is try to minimize the value in SS Resids. Once you have the smallest value you think possible, click on Show Best Line to see how well you did.