The following predefined constants are useful for conversion between units
| Name | Value | Conversion from | Conversion to |
| DEG2RAD | \(2 \pi / 360\) | Degrees | Radians |
| RAD2DEG | \(360 / (2 \pi )\) | Radians | Degrees |
| MIN2RAD | \(2 \pi / (360 \cdot 60)\) | Minutes of arc | Radians |
| RAD2MIN | \((360\cdot 60) / (2 \pi )\) | Radians | Minutes of arc |
| FWHM2RMS | \(1/\sqrt {8\log (2)}\) | Full width half maximum | Root mean square (standard deviation) |
| RMS2FWHM | \(\sqrt {8\log (2)}\) | Root mean square (standard deviation) | Full width half maximum |
| PI | \(3.14159265...\) | \(\pi \) |
|
| CELE | 1.602176487e-19 | Elementary charge (C) |
|
| M_C | 299792458 | Speed of light in vacuum (m/s) |
|
| MELECTRON | 9.10938291e-31 | Electron mass (kg) |
|
| ALPHA | 7.2973525698e-3 | Fine structure constant, \(\alpha \) |
|
| RE | 2.8179402894e-5 | Thomson scattering length (AA) |
|
| E2K | 0.506773091264796 | Energy (keV) | Wavenumber (1/AA) |
| K2E | 1.97326972808327 | Wavenumber (1/AA) | Energy (keV) |