Exact Center Freq is an optional field for the frequency usage plot on Multi Maps. This is the exact frequency that you currently have this transmitter operating on. This can be found in the Transmission Site Transmitter info section of your coverage settings.
For Example: You have selected WIFI 2.4 GHz for your frequency band and this antenna is operating at channel 2417. You may choose to enter 2417 in the Exact Center Freq field. Again, this is not a required field for TowerCoverage.com. Entering the exact frequency of this coverage can help you see possible interference on your own network.