At microwave frequencies, use the app to determine the skin depths of aluminum copper gold or silver and others. Use the checkboxes next to the metal to select it, then enter the frequency then push the "Calculate" button. For f = 10 your results should be 8. 15E-7 for Al, 6. 6E-7 for Cu, 7. 86E-7 for Au and 6. 41E-7 for Ag.