  Despite 180 years of theory on magnetism, it appears that the practice of
calculating forces on magnetic media is ambiguous, as illustrated by a recent
article by Casperson. Potentially troubling issues include: Which field B or H
should be used? Should the total field be used, or only the external field? And
if the latter, what is meant by "external"? Can/should effects of magnetization
currents and/or fictitious magnetic poles be included? What is the force on
only a portion of a circuit? We review several well-known approaches to
magnetic force calculations on elements of rigid circuits, and find it very
helpful to use an explicit example to compare and contrast the various methods.
