Sub CORREL(DATA1(), DATA2(), N, ANS())
    Dim FFT(128)
    Call TWOFFT(DATA1(), DATA2(), FFT(), ANS(), N)
    NO2 = N / 2#
    For I = 1 To NO2 + 1
      DUM = ANS(2 * I - 1)
      DUM1 = FFT(2 * I - 1) * DUM + FFT(2 * I) * ANS(2 * I)
      ANS(2 * I - 1) = DUM1 / CSng(NO2)
      DUM2 = FFT(2 * I) * DUM - FFT(2 * I - 1) * ANS(2 * I)
      ANS(2 * I) = DUM2 / CSng(NO2)
    Next I
    ANS(2) = ANS(N + 1)
    Call REALFT(ANS(), NO2, -1)
    Erase FFT
End Sub