Experimental techniques continued measurement uncertainties

To understand this discrepancy, we need to remember that there is a second source of error in any experiment systematic error that causes a shift in the measured values from the true value and reduces the accuracy of the result. By making more measurements, we can reduce the uncertainty due to random errors and improve the precision of our result however, if systematic errors are present, the average value will continue to deviate from the true value. Such systematic errors may result from a miscalibration of the experimental apparatus or from a fundamental inadequacy in the technique for measuring a property. In the case of Millikan s experiment, the then-accepted value for the viscosity of air (used in calculating the charge e) was subsequently found to be wrong. This caused his results to be systematically too high. 

O Neal and Benson have carried out a detailed analysis of the entropies and heat capacities of alkyl free radicals, and we refer the reader to their work. It is worth noting that entropies and heat capacities for free radicals are not measured directly, but either calculated by one of the techniques outlined earlier or inferred from experimental kinetic measurements in conjunction with some calculations. Principal sources of uncertainty in such calculations have been, and continue to be, questions of structural symmetry and barriers to internal rotations in the radicals. The calculation of butyl radical illustrates both of these uncertainties. O Neal and Benson and later Benson assumed that the radical site in planar, and thus has a symmetry number <7 = 162 (6 for... 

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