Sometimes the different sets of data in a combination chart are so different that they need a bit more clarification. In the first chart here, the columns show the sales revenues (dollars, that is, not cases) for Teatime Chocolate Biscuits. The Line chart shows the commissions for the salespeople, calculated on the basis of the sales revenue. The value of the commissions is only a small percentage of the value of the sales. Even though they are shown differently, you cannot make out the smaller values.
You can solve this problem by adding another, secondary, chart axis. Plotting the values of the commissions on their own axis makes it easy to understand the Line chart, as you can see in the second chart shown here. Peacock received a commission of about $9,000, Davolio about $2,700, and Suyama about $18,000.
To create a secondary axis, you'd select the chart type that you want that axis for, and then you'd make a few selections in the Format Data Series dialog box. You'll learn the steps in the practice session.