Yes, this post will be primarily a copy of a Harvard Business Review (HBR) article. The article is the point of this blog. Over my decades in consulting, one of the major requirements in our niche was to insure that our clients received the savings we had forecast that they would achieve in a mutually agreeable manner. In the very beginning, when I started back in 1974, computers were not easily available or accessible as they had to be huge room-size machines and many clients did not even have them. So we used adding machines with paper tape to the shortly thereafter personal hand held-calculators. Personal computers starting with the very first Apple or Radio Shack model proved far superior but had minimal calculating capacity. None were perfect and because of this limitation, a straight line average over a years period was typically used to compare history to current and prove savings had been achieved. I found well into my career that straight-line bases had fallacies in the