This thesis is aimed to analyze the effect of test parameters on DRM results from OLTC and its implementation in the condition assessment. Two test parameters were selected to be observed, which are test current and circuit resistance. Their amplitude was varied during the measurements and experiments in the laboratory as well as in the field (substation). To quantify the measurement results, an analytical tool was introduced. Its purpose is to convert the DRM results into 4 parameters. They are plotted as curves, in such a way that particular behaviours of the curves determine the influence of the test parameters. Further on, the influence of test parameters has been utilized to determine an optimum level of test parameter. It is used to conduct the measurement to gain reliable results. Then with the help of three dimensional classification system, the actual condition of OLTC can be identified. It shall simplify the condition assessment of OLTC.