Fiber Bragg grating (FBG) sensors are prone to spectral distortions in practical applications, which may cause large demodulation errors. There are many algorithms demodulating FBG spectra, but no approach is able to evaluate demodulation results under spectral. Fibre Bragg grating (FBG) sensors are used to measure various quantities such as temperature, stress, vibrations, pressure, or refractive index. Their most important advantage is signal modulation consisting in shifting the spectrum in the wavelength domain. By changing the step size of each calculation.