1. Find the prediction line and notice what the slope and intercept are. The slope will be 0. The initial value of the intercept will be the mean of Y. Also locate the values of SSE and MSE.
   
2. Move the line up by clicking and holding in the middle of the line and then dragging it up. Notice that the intercept increases as you move the line up. The slope does not change.
   
3. Notice how the MSE (which indicates how close the line comes to the points) changes as the intercept changes.
   
4. Make the slope positive by clicking and holding on the left edge of the line and dragging the line down. Check the slope to make sure it is positive.
   
5. Reduce the slope by clicking and holding on the right edge of the line and dragging down.
   
6. Change the slope so as to get the lowest MSE you can get. Then change the intercept to see if you can lower the MSE further. Then change the slope again.
   
7. Click the "Show regression line" button and see how close your prediction line is to the best-fitting line. Compare the MSE's of the two lines.
   
8. Click the "new data set" button and find the best fit you can. Compare this to the best-fitting line.
   
9. Repeat the previous step several times.