Purpose: to provide a correlation between two time series (2 WFs). Outcome: Pearson's Product Moment correlation coefficient (r) shows
positive, zero or negative correlation. Cross-correlation repeats this test
at a number of "lags", shifting one series progressively left or right of the
other, to show stability of phase relationships. Procedure: Rectify and filter ENGs, select data range, downsample
data, cross-correlate and plot. Examples: Combining two cross-correlations on the same graph,
creating a cross-correlation histogram figure using Excel.