1. A method for monitoring a manufacturing operation, said method comprising: performing multiple runs of a processing operation upon semiconductor substrates over time, said processing operation having a measurable impact on a characteristic of said semiconductor substrate; measuring said characteristic at a plurality of sites on said corresponding semiconductor substrate for each said run; identifying an outlier site of said plurality of sites wherein said measured characteristic has the largest or smallest average value over said runs; and generating a comparative index comparing a value of said measured characteristics of said outlier site to a value of said measured characteristics of other sites of said plurality of sites, for each said run, wherein said characteristic comprises one of sheet resistance, resistivity, specularity and refractive index, and further comprising monitoring said generated comparative index for each said run, over time, and adjusting said processing operation based on trends or changes in said comparative index over time.