2. Apply carb heat and observe engine rpm: If there is an immediate drop in rpm and no other indications, select cold and look for an immediate return to cruise rpm. The engine is free of ice ... continue for another ten minutes.
Now then there will be people who will disagree with that, our CFI for one. No good asking me to explain, I don't understand complicated stuff. He reckons that the carb heat should be out for a minimum of thirty seconds on the FREDA check, in fact increase the RPM a little first before you apply carb heat. He's not a newbie CFI either, he's ancient and has squillions of hours on squillions of types.