The physical constants are in the Phys menu, Constant sub-menu. The following table gives the Constants Library :
| Name | Description |
| _NA_ | Avogadro’s number |
| _k_ | Boltzmann constant |
| _Vm_ | Molar volume |
| _R_ | Universal gas constant |
| _StdT_ | Standard temperature |
| _StdP_ | Standard pressure |
| _sigma_ | Stefan-Boltzmann constant |
| _c_ | Speed of light in vacuum |
| _epsilon0_ | Permittivity of vacuum |
| _mu0_ | Permeability of vacuum |
| _g_ | Acceleration of gravity |
| _G_ | Gravitational constant |
| _h_ | Planck’s constant |
| _hbar_ | Dirac’s constant |
| _q_ | Electron charge |
| _me_ | Electron rest mass |
| _qme_ | q/me (Electron charge/masse) |
| _mp_ | Proton rest mass |
| _mpme_ | mp/me (proton masse/electron masse) |
| _alpha_ | Fine structure constant |
| _phi_ | Magnetic flux quantum |
| _F_ | Faraday constant |
| _Rinfinity_ | Rydberg constant |
| _a0_ | Bohr radius |
| _muB_ | Bohr magneton |
| _muN_ | Nuclear magneton |
| _lambda0_ | Photon wavelength (ch/e) |
| _f0_ | Photon frequency (e/h) |
| _lambdac_ | Compton wavelength |
| _rad_ | 1 radian |
| _twopi_ | 2*pi radians |
| _angl_ | 180 degrees angle |
| _c3_ | Wien displacement constant |
| _kq_ | k/q (Boltzmann/electron charge) |
| _epsilon0q_ | epsilon0/q (permitivity /electron charge) |
| _qepsilon0_ | q*epsilon0 (electron charge *permitivity) |
| _epsilonsi_ | Silicium dielectric constant |
| _epsilonox_ | Bioxyd of silicium dielectric constant |
| _I0_ | Reference intensity |
To have the value of a constant, input the constant name in the command line of Xcas and valid with enter (don’t forget to put _ at the begining and at the end of the constant name).