The radius axis on a polar chart can be formatted just like any other value axis, but you will also find some setting on the Other tab, available from the Plot menu item in the Chart Designer dialog box.

Scaling the polar axis lets you to control the number of radial grid lines and labels that are displayed around the perimeter of the chart. Radial grid lines for major divisions extend to the center of the chart. Radial grid lines for minor divisions extend from the first division of the value axis to the perimeter of the chart.