Additive Offsets

Some systematic errors, instead of taking the form of a constant ratio of measurements to true values, take the form of a constant difference between measurements and true values; these systematic errors are additive, not multiplicative. During the experiments presented in this thesis, the apparent electron arrival rates (chapter 5) at the detectors, with the electron gun switched off, and the conditions otherwise the same as in the real experiments, were occasionally checked. These rates should indicate the size of any additive systematic error. They were found to be of the order of $1\,\mathrm{Hz}$, which is much smaller than the measured rates with the electron gun on. Additive systematic errors are, therefore, not believed to be significant here.