S50: Switch Setttings
The 1,2,3 switches and the A,B switches are configuration settings. The S50 comes pre-configured for most kinds of telephones. However, if your headset has acoustic problems, you may need to adjust them. Remove the telephone hand receiver from the base of the telephone, and put on your headset. Then simply start with position 1 and try A or B, position 2 and try A or B, and lastly position 3 and try A or B. The position with the loudest sound is the correct setting for your telephone.
Please note that this product has been discontinued in North America.