New results in spectral interferometry are presented. The effect of imperfect calibration of the optical spectrometer is demonstrated both theoretically and experimentally. It is shown in particular that slight calibration imperfections can lead to mistakes because of the principle of spectral interferometry itself. Efficient methods are demonstrated to overcome this problem and to provide spectrometer calibration with a precision far superior to the instrument's optical resolution. Results for spectral phase interferometry for direct electric-field reconstruction are also demonstrated. (C) 1999 Optical Society of America [S0740-3224(99)02207-9].