Gradually turn up th eheat until you see a noticeable reaction. When you get a reaction from th edog stop. Use the heat to correct an action but he does not respond turn it up untill he responds. Hold the heat untill he stops doing what he is not supose to be doing. He needs to learn that id he does some thing he is not supose to that the heat will stop when he acrts correctly.
Example: i set mine at 3, for that is the heat he responds to. Yesterday he took off after another dog (wanting to play) and i called him back, he did not listen so increased the heat a little at a time untill he responded to the heat (shock). Unfortunatly it was up to full power before he responded and i felt bad that i gave him so much heat, but that is what it took to get the proper responce from him. After that, turned it back down to the normal settings.
Hope this helps. (this is how i was explained to use it by my trainer)