Analysis of the inconsistency between two interpolations of the water-tin and water-aluminum sub-ranges of the ITS-90

This paper has two purposes: the first is to determine the magnitude of the inconsistency in the overlap region of the water-aluminum and water-tin sub-ranges through investigation of calibration of the SPRTs. The other is to understand the characteristic of the inconsistency function in the region. In this paper, twenty one SPRTs were investigated. The results show that their inconsistencies are in the range from −1.26mK to 1.22mK except one of them is 4.08mK. The inconsistency function between the ITS-90 interpolations in the overlap region is unique cubic polynomial function with a movable real root, different from other inconsistency functions. By means of factoring, this paper gives an alternative form of the inconsistency function and makes an analysis of the roots and extrema of the function.