The friction of roads is a test statistic that can be described by various kinds of test methods. These test methods often base on different measuring principles. The aim of friction measuring is to provide an assessment of the quality of road sections. To check the quality of these sections, the measuring results must be compared with prescriptive limits. Are these measuring results higher than the limits, the quality of the road section is good. Are the measuring results lower than the limits, the quality of the section is bad. In the majority of cases, various testing methods lead to different results. If there is only one list of prescriptive limits, the assessment of these various testing methods is not equal. The test methods Seitenkraftmesser (SKM) and GripTester are in the focus of this work. The SKM method has already got prescriptive limits. But there are no final prescriptive limits for the GripTester method. The aim of this work is to develop prescriptive limits for the GripTester which do not contradict those results gained by the SKM method. A calibration line describes the technical correlation between the inspection characteristics of both, SKM and GripTester. By means of this calibration line, the prescriptive limits of the SKM can be transformed to those of the GripTester. The evaluation of the calibration line is based on a harmonized database of different measuring campaigns. In the first step, a model of data harmonization has been developed. The data base has been split into classes of elements with equal characteristics. For these classes specific calibration lines have been calculated. But none of these calibration lines may describe the technical combination completely. Measure point variances round the calibration line have been detected. The reason for these variances partly lies in the method of combining the inspection characteristics. The variances are the result of both systems, the SKM and the GripTester. But there are fixed standards for the prescriptive limits for the SKM method. Therefore the variances in the prescriptive limits of the GripTester have to be considered. For a proved assessment by the GripTester, the prescriptive limits with the variances between SKM and GripTester must be increased. This is, the prescriptive limits of the GripTester must be higher than those of the SKM. As a result of this work, prescriptive limits for the GripTester have been defined. Is the measuring result higher than the prescriptive limit, the quality of the road section is good. Has the quality been measured by the GripTester, it is most likely that the SKM reports a good quality too. But when the GripTester reports a bad result, it is not possible to conclude the SKM quality assessment.