Discussion of correlation for the combined standard uncertainty evaluation

Sometimes the correlation of those input quantities is hardly to avoid,the correlation coefficient quantitative expresses the degree of correlation,which could be obtained either experiment with measuring methods or analysis of theory.When these input quantities were correlative,the combined standard uncertainty could not calculated if the correlation coefficient was unknown.The paper introduces the methods of correlation coefficient evaluation and the common principles of correlation to deal with,also the paper emphasized to discuss the reason of making correlation and analyses to the several occasions either of correlation or no correlation.Finally,the paper applies the partical example to give the process of application.