Thank you again UH. I do take this on faith since I understand the purpose of the total energy compensation and I can see its effects. Unfortunately, students sometimes ask 'how'. I feel I must avoid talking nonsense when they ask. So far I have just replied that I do not know 'how' but I do know 'what'. After several such experiences my own curiosity has led me to try to understand 'how'. I guess I can't help myself!