Since the first edition there have been many changes in the equipment available for measurements and the growing interest in Transmission Error measurement has spawned numerous approaches that are not always clearly described. Each author has a tendency to extoll the virtues of his approach but rarely points out the corresponding disadvantages, so I have attempted to compare systems. A range of new problems in from industry has generated some interesting additional topics.
I have also added discussion of some of the less common but puzzling topics such as high contact ratio gears which are increasingly being used to reduce noise. Testing procedures are also discussed in more detail together with some practical problems and some slightly extended description of the failures that may be encountered and their relationship, or lack of it, to noise problems.