More and more, natural scientists are becoming aware that they must consider the human element as one of the variables in physical measurement. Its measure has usually been hidden in what has been called the error of measurement. Part of its measure has been qualitative for we often hear that Mr. Soandso is a good or a poor experimenter or observer. As we go to engineering research or to any applied field, we become more conscious of the human element. Here, an attempt is made to design apparatus and measuring equipment that will operate or make measurements with minimum variability associated with people. Some problems, such as those dealing with what consumers want, require an even more complete knowledge about the behavior of people. It is not possible to define or to specify a product that will be satisfactory to the consumer if we do not know what the consumer wants. Hence, it is our first observation that the natural scientist needs information about the human element that is always present to some degree in his work.