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## Main Question or Discussion Point

In Hartle's book on General Relativity, page 47 footnote 1, it says: "You might be used to thinking that quantities called [itex]\epsilon_0[/itex] and [itex]\mu_0[/itex] are the basic parameters in Maxwell's equations, but [itex] \mu_0 \equiv 4\pi \times 10^{-7}[/itex] is a pure number, and [itex]\epsilon_0 = 1/(c^2 \mu_0)[/itex]."

But as far as I know permeability of free space does have units, for example:

http://scienceworld.wolfram.com/physics/PermeabilityofFreeSpace.html

But as far as I know permeability of free space does have units, for example:

http://scienceworld.wolfram.com/physics/PermeabilityofFreeSpace.html

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