Enter the grating number, selecting among : 150, 300, 600, or 1200. The default diffraction order is set to 1. Then, choose the central wavelength (in Angstroms) and finally enter a slit width (in arcsec). This form calculates the corresponding grating angle (in degrees), the dispersion at the central wavelength (in A/px) and the spectral range. Besides, it converts the angular value of the slit width in microns units and calculate the spectral resolution (in Angstroms), based on the Nyquist criterion.