according to the idea that one cannot hit out of anger, but should only potch out of the desire to be mechanech, one who hits his child should be able to IMMEDIATELY give him a hug/kiss and say I love you. this is to convey that the child did something dangerous/wrong, is not violence (since there is no force behind it–in the case of anger, there is force), and leaves the child still feeling loved and safe. this is the proper way to administer potches.
if one is too worked up and cannot bring himself to hug his child after potching him, he can be sure that he was not mechanech correctly. no one ever said its ok to take your annoyance out on your child.