def autocorrelation_plot(time)
      r = autocorrelation time
      start = @times[:repeat].first
      ende = (start + r.size)
      (start...ende).to_a.zip(r)
    end
def autocorrelation_plot(time)
      r = autocorrelation time
      start = @times[:repeat].first
      ende = (start + r.size)
      (start...ende).to_a.zip(r)
    end
Returns the arrays for the autocorrelation plot, the first array for the
 numbers of lag measured, the second for the autocorrelation value.