A system and method for detecting an endpoint during a chemical mechanical polishing process is disclosed that includes illuminating a first portion of a surface of a wafer with a first broad beam of light. A first reflected spectrum data is received. The first reflected spectrum of data corresponds to a first spectra of light reflected from the first illuminated portion of the surface of the wafer. A second portion of the surface of the wafer with a second broad beam of light. A second reflected spectrum data is received. The second reflected spectrum of data corresponds to a second spectra of light reflected from the second illuminated portion of the surface of the wafer. The first reflected spectrum data is normalized and the second reflected spectrum data is normalized. An endpoint is determined based on a difference between the normalized first spectrum data and the normalized second spectrum data.