Readers will by now probably be bewildered at the complexities described in this chapter. After all, there could scarcely be a simpler notion than that of the torque experienced by a magnet in a magnetic field, and there would seem to be no need for all of these complicated variations. You are right – there is no such need. All that need be known is summarized in Sections 17.2 and 17.3. The difficulty arises because authors of scientific papers are using almost all possible variations of what they think is meant by magnetic moment, and this has led to a thoroughly chaotic situation. All I can do is to hope that readers of these notes will be encouraged to use only the standard SI definition and units for magnetic moment, and to be aware of the enormous complications arising when they depart from these.