Abstract: The influences of a non-perpendicular diffraction on the wavelength are discussed in three aspects. The figures are plotted by using the Mathematica program,the error is evaluated and compared with the influence of the instrument permitted error.We conclude that some of the adjustments of the spectrometer are necessary,and some are due to the purpose of training.

Key words: diffraction grating, non-perpendicular, wavelength, influences, Mathematica