= Uniform magnetic field in an off-axis cylindrical cavity
{title2=$\mathbf B=\mu_0\mathbf J\times\mathbf b/2$}
Subtract a cylinder of <current density> $\mathbf J$ occupying the cavity from a complete current-carrying cylinder. Inside each cylinder, $\mathbf B=\mu_0\mathbf J\times\mathbf r/2$. The difference is independent of observation point and equals $\mu_0\mathbf J\times\mathbf b/2$, where $\mathbf b$ is the offset of the cavity axis. This assumes parallel axes, uniform <current density> in the remaining metal, and negligible end effects.
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