The constant $\textit{Magentic Constant}$, also known as $\textit{Permeability of Vacuum}$, is a scalar constant
$\mu_0$ such that, in a vacuum the product with the magnetic field vector, $\overrightarrow{H}$
is equal to the magnetic flux density vector, $\overrightarrow{B}$.
http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=31891
http://physics.nist.gov/cuu/Constants/bibliography.html
http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=705-03-14
http://dbpedia.org/resource/Vacuum_permeability
$\mu_0 = \frac{\overrightarrow{B}}{\overrightarrow{H}}$, where $\overrightarrow{B}$ is the B-Filed magnetic vector, and $\overrightarrow{H}$ is the H-Filed magnetic vector. The value of $\mu_0$ is $\approx 1.256637e-6\,H/M$.