Sidetone is the level of your own voice that you hear while talking on the intercom. Setting a comfortable level of sidetone will ensure that the intercom line sounds alive and also helps you modulate your voice relative to other voices on the line.  Typically, different sidetone null settings are needed depending upon whether you are using the speaker. Use one of the following procedures to correctly set the sidetone level control on KB-702GM panel which is capable of supporting a gooseneck mic / speaker or a headset. 
Sidetone Adjustment Procedure for Headset:
1. Set the intercom level volume control to a comfortable level by having someone talk to you from another station.
2. Press the talk button and speak into the microphone while turning the sidetone null control slowly back and forth until you hear your voice at a comfortable level in the headset.
Sidetone Adjustment Procedure for Gooseneck Mic (KB-702GM only) or hand-held push-to-talk mic with the speaker turned on:
1. Set the VOX control fully counterclockwise to disable this feature.
2. Set the intercom level volume control to a comfortable level.
3. Press the talk button and speak into the microphone while turning the sidetone null control slowly back and forth.
There should be a point where your voice (and any accompanying acoustic feedback) disappears. 
This is the null point.