Clinical analyses have a vital importance in human health. Thus, it is necessary to have reliable analytical information which depends on a good assessment of accuracy and this can be obtained by minimization of uncertainty values, The uncertainty values are complex and arise from different sources such as sample, method, instrumentation and data processing. Some of these components may have been evaluated from the distribution of results of series of measurements and can be characterized by standard deviations. In our laboratory, for example the balance calibration uncertainty for 1g was found to be 0,00414g. The uncertainties for the volume of solution contained in a 100mL volumetric flask and a 0.5 mL glass-pipette were calculated to be 0.0843mL and 0.0071 mL respectively and etc.