Spectrometer calibration is an essential step for all spectroscopic applications. All our spectrometers are calibrated during production and quality control (QC). This process is carried out using calibration light sources with known spectral lines. During this process, light from a calibration light source (the choice of which depends on the configuration of the spectrometer to be calibrated) connected to the spectrometer, passes through various optical elements, including a dispersive grating, and eventually reaches the array detector. After calculating the peak position on the detector, the positions and intensities of the peak pixels are used to find the relationship between the position of the peak pixels and their wavelengths. This relation or wavelength calibration can be fitted by linear regression or low-order polynomial (or even 5th order, for example, by Bocklitz T., Dörfer T., Heinke R., Schmitt M., et al.). Recent publications also present wavelength calibration methods based on the physical model of the optical path in the spectrometer, as well as some improvements to the calibration procedure, e.g., using noise reduction, stray light removal, improved peak position estimation by peak shape fitting with Voigt function, Gaussian or Lorentzian, etc.