oops................in last response i used the term Shock Wave, I believe the term is Soft Wave..........i once told a friend, if you ask me a question and I give an answer, ask me again the next day, as, i used to be able to snap out correct answers, but at my age of 82, i am finding that, some of my answers, are sometimes , not what i really meant:) and a day later, i clarify them.