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According to the combination of theory and practice, a precision measurement of roller chain length was expounded. The preparation of the muster, installation of the sample, instruction in experiment, and disposal of experiment data were also indicated. And eight-spot measurement in chain length precision measurement of chain industry was put forward for the first time. It proved by the practice that the measurement is very important in unification of experiment criterion of chain industry, advancing scientificity and veracity of chain length precision measurement.