I have a digital thermostat that keeps the temperature on the exact degree on which it is set. If, for example, it is set on 70, it operates often enough that the temperature stays a constant 70. I have friends who say their thermostat varies a couple of degrees. In the heating season, for example, they set it on 70 and it drops to 68 before kicking back on to reach 70 again. Is that more efficient than the way my thermostat operates and is there a way of programing one to do that? Thanks.