Weight loss is a method for measuring MRR, which is not an efficient method for a tiny sample such as sapphire or SiC wafer having mass of about 1g or 300 mg per wafer. This is because of unavailability of a very high precision weight balance machine. In addition, sometimes the samples are mounted by automatic mounting machine using resin. So, it is inevitable to find an efficient method to measure MRR accurately as much as possible.