It is a well recognized fact that the successful operation of any machine depends upon the ability and knowledge of the operator. Usually, the manufacturer has no responsibility for, or control over, the selection of the operator, and therefore cannot be responsible for the ability of that operator. On the other hand, the ability of the operator is directly dependent upon his knowledge of the machine, and it is the responsibility of the manufacturer to make available such information concerning his product as is necessary for its intelligent operation.

In presenting this book, RCA PHOTOPHONE, INC. aims not only to present a comprehensive description of its apparatus, but also to give in elementary terms an understanding of the operation of this apparatus. Such technical information as may prove of assistance in the understanding of the various operational procedures is given, but deeply involved technical discussions have been avoided as far as possible.

In addition to explaining the "how" and "why" of the operation of PHOTOPHONE equipment, it is also our aim to give this information in such a fashion as to enable the projectionist to intelligently recognize, locate and remedy such minor defects as might occur during the operation of the equipment, and make whatever minor adjustments which may become necessary for the proper operation of the equipment.

To those whose previous training does not qualify them for an exact understanding of the theory involved, we wish to state that it is not necessary to understand in detail this theory in order to have a practical working knowledge of the apparatus. Such theoretical discussions as may be found in this book serve merely to explain the reasons why certain things are done.

---