Methods and systems for monitoring a parameter of a measurement device during polishing, damage to a specimen during polishing, a characteristic of a polishing pad, or a characteristic of a polishing tool are provided. One method includes scanning a specimen with a measurement device during polishing of a specimen to generate output signals at measurement spots on the specimen. The method also includes determining if the output signals are outside of a range of output signals. Output signals outside of the range may indicate that a parameter of the measurement device is out of control limits. In a different embodiment, output signals outside of the range may indicate damage to the specimen. Another method includes scanning a polishing pad with a measurement device to generate output signals at measurement spots on the polishing pad. The method also includes determining a characteristic of the polishing pad from the output signals.