The spectral classification code Diagnose assigns one of four classifications (star, galaxy, quasar, or unknown) to each source and returns a redshift estimate for the galaxies and quasars and a velocity estimate for the stars. The code uses a chi-squared minimization for linear combinations of principal component templates to determine a best-fit spectral classification and redshift estimate. It computes three best-fit chi-squared values: one for stellar type and velocity, one for galaxy type and redshift, and one for a quasar and redshift. Diagnose then compares the best fit of these three reduced chi-squared values to the second best fit and evaluates the difference against a statistical threshold.