The GetConstant( descriptor ) command returns the definition of a physical constant in the ScientificConstants package.

For a nonderived physical constant, the expression sequence returned consists of the constant's full name followed by equations that specify its symbol, value, uncertainty, and units.

For a derived physical constant, the expression sequence returned consists of the constant's full name followed by equations that specify its symbol and derivation derive.

The right-hand side of the derivation equation is an expression that gives the derivation of the constant in terms of other physical constants, using their currently defined symbols.

The expression sequence returned is in the same format used for the AddConstant function.

$\mathrm{with}\left(\mathrm{ScientificConstants}\right)\:$

$\mathrm{GetConstant}\left(G\right)$

$\mathrm{Newtonian\_constant\_of\_gravitation},\mathrm{symbol}=G,\mathrm{value}=6.67408\times {10}^{\mathrm{-11}},\mathrm{uncertainty}=3.1\times {10}^{\mathrm{-15}},\mathrm{units}=\frac{m^3}{\mathrm{kg}{s}^2}$

$\mathrm{GetConstant}\left(m\left[e\right]\right)$

$\mathrm{electron\_mass},\mathrm{symbol}=m_e,\mathrm{derive}=\frac{2R_{\mathrm{\infty }}h}{c{\mathrm{\alpha }}^2}$