For example, Figure shows the raw mass spectrometer (MS) data and the amplitude spectrum plot for the 0.001 Hz and 0.3 Hz experiments used in run 3 from Figure . The amplitude spectrum plot, produced by the FFT algorithm in MATLAB, represents the raw MS signal (Figures and) as a series of sinusoids and plots the amplitudes of these as a function of frequency. This plot can be considered the amount of each frequency in the signal. Therefore, the amplitude spectrum of a clean square wave should have peaks at the primary frequency and odd integer multiples of this frequency. The raw MS data in Figures and is converted to amplitude spectrum data in Figures and, as described above. At 0.001 Hz (Figures and), many harmonics could be used since many peaks are located at odd integer multiples of the main frequency. However, at 0.3 Hz (Figures and), only 2 harmonics were used (1 st and 3 rd ). This occurs because, as shown in Figure , the square wave at 0.3 Hz generated by the mass flow controllers is not perfectly square. Therefore, the transform of this data produces a small peak at an even interval, as shown in 3d by a red circle. Since an even interval peak can not exist per equation 2, all peaks lower than this amplitude were neglected, resulting in the 1 st and 3 rd harmonics being used for 0.3 Hz. Additionally, to reduce scatter on the plots caused by using many harmonics, as was seen in Figure , at most, 4 harmonics per square wave are used in the remainder of this work. However, more harmonics could be used, provided peaks can be identified at odd integer multiples of the principle frequency, while small or ideally no peaks exist at other frequencies, as in Figure .