The top-selling products widget tries to show you sales volume on a product basis.
The start view shows you your top-selling products based on total revenue per product. You can click the dropdown to show the top products based on units sold if you wish.
The scatter chart is a combination of revenue and the number of units sold. The Y-axis represents revenue and the X-axis represents units sold, and the product will be placed into the chart where the lines for a product intersect.