As reason replaces instinct in the development of mankind, much is gained. However, when one reads of the meteorologist, snowbound in an unpredicted storm, or sees with wonder how the robin annually beats an unfaltering 2000-mile course without chart or compass, one ponders the dubious advantages of the rational mind. An engine, they tell us, is the product of cold mathematical design reasoning, as inflexible as Newton's Laws, and it should act that way. But, to the test engineer, it sometimes appears as flighty and unpredictable as a prima donna at a public relations conference. En masse, they are even more capricious, acquiring individualistic qualities that challenge the best efforts of the inspector, as though in a deliberate effort to disprove the assumed equality of mass production birth. Perhaps the almost human qualities of engines account for the outstanding success of that early automotive test artist -- the tune-up man, who instinctively knew where to set the spark, and brought out the best in a carburetor, with much the same approach as a violinist produces true notes from a string. Perhaps, as engines become more complex and the supply of test artists more scarce, we are losing something not merely nostalgic when we are forced to substitute the science for the art. Our purely reasonable approach may never be completely successful. So, before we embark on a discussion purported to describe some scientific approaches to engine testing, we make a sincere bow to the artists, who, without measuring the frequency instinctively produced the music.