The Constant( descriptor ) command constructs a physical constant object. The object can be used, for example, to access the value, see GetValue, or the uncertainty in its value, see GetError.

If no options are specified, an object is returned with no system of units. When such an object is evaluated or queried, it returns the physical constant value in the current system of units. For more information, see Units[UsingSystem].

If the 'units' option is specified and the 'system' equation is not specified, the units are selected from the current system of units.

To access the value of an object with units, use the evalf function.

The opts argument can contain one or more of the following equations that set object options.

'system' = symbol

This option controls the system of units associated with the object. If the system specified is a system of units accepted by the Units package, the returned constant object has the system of units specified in index notation. For a list of accepted systems of units, see Units/Systems. When such an object is evaluated or queried, it returns the physical constant value in the indicated system of units.

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

$\left[\mathrm{AddConstant}\,\mathrm{AddElement}\,\mathrm{AddProperty}\,\mathrm{Constant}\,\mathrm{Element}\,\mathrm{GetConstant}\,\mathrm{GetConstants}\,\mathrm{GetElement}\,\mathrm{GetElements}\,\mathrm{GetError}\,\mathrm{GetIsotopes}\,\mathrm{GetProperties}\,\mathrm{GetProperty}\,\mathrm{GetUnit}\,\mathrm{GetValue}\,\mathrm{HasConstant}\,\mathrm{HasElement}\,\mathrm{HasProperty}\,\mathrm{ModifyConstant}\,\mathrm{ModifyElement}\right]$

$\mathrm{Constant}\left(g\right)$

$\mathrm{Constant}\left(g\right)$

$\mathrm{GetValue}\left(\right)$

$9.80665$

$\mathrm{GetUnit}\left(\right)$

$⟦\frac{m}{s^2}⟧$

$\mathrm{Units}:-\mathrm{UsingSystem}\left(\right)$

$\mathrm{SI}$

$\mathrm{Constant}\left(g\,\mathrm{units}\right)$

${\mathrm{Constant}}_{\mathrm{SI}}\left(g\right)⟦\frac{m}{s^2}⟧$

$\mathrm{Constant}\left(g\,\mathrm{system}=\mathrm{FPS}\right)$

${\mathrm{Constant}}_{\mathrm{FPS}}\left(g\right)$

$\mathrm{GetValue}\left(\right)$

$32.17404856$

$\mathrm{GetUnit}\left(\right)$

$⟦\frac{\mathrm{ft}}{s^2}⟧$

$\mathrm{Constant}\left(g\,\mathrm{system}=\mathrm{FPS}\,\mathrm{units}\right)$

${\mathrm{Constant}}_{\mathrm{FPS}}\left(g\right)⟦\frac{\mathrm{ft}}{s^2}⟧$

$\mathrm{evalf}\left(\right)$

$32.17404856⟦\frac{\mathrm{ft}}{s^2}⟧$