We present product wafer and laboratory test results of a production worthy, in situ, broadband optical endpoint system in the context of a simple model that describes the reflectance of semiconductor wafers during chemical mechanical planarization. Broadband and single wavelength approaches are presented. The challenges of extracting precise endpoint measurements on patterned product wafers in an intrinsically noisy environment are addressed. Finally, the benefits: of using such an endpoint system are presented. Experimental data on tungsten, copper, shallow trench isolation. and interlevel dielectric layers is presented.