It depends on if you have a Heat Pump, Single stage or two stage system. You press Menu, then press the "Swing" icon and set for what you wish. I have my swing set for 1.5. Differntial is set for 3.0, due to I have a Two Stage furnace, but Single Stage A/C. Setting the Differential to 3.0, allows my furnace to run at a lower speed to cool the house better and draw off not as much humidity.
If your system is doing what is called "Short" Cycling. It may be that the thermostat was setup incorrectly for the type of system you have. You can download the Installation manual for the thermostat at http://www.radiothermostat.com/support.html. The one you want is for the CT-30 model. The CT-80 operation manual explains about Swing & Differential settings.