Function BESSY1(X)
    P1 = 1#:                     P2 = 0.00183105
    P3 = -0.00003516396496:      P4 = 0.000002457520174
    P5 = -0.000000240337019
    Q1 = 0.04687499995:          Q2 = -0.0002002690873
    Q3 = 0.000008449199096:      Q4 = -0.00000088228987
    Q5 = 0.000000105787412:
    R1 = -4900604943000#:        R2 = 1275274390000#:
    R3 = -51534381390#:          R4 = 734926455.1
    R5 = -4237922.726:           R6 = 8511.937935
    S1 = 24995805700000#:        S2 = 424441966400#
    S3 = 3733650367#:            S4 = 22459040.02
    S5 = 102042.605:             S6 = 354.9632885
    S7 = 1#
    If X < 8# Then
        Y# = X ^ 2
        AAA# = R1 + Y * (R2 + Y * (R3 + Y * (R4 + Y * (R5 + Y * R6))))
        BBB# = S4 + Y * (S5 + Y * (S6 + Y * S7))
        BBB# = S1 + Y * (S2 + Y * (S3 + Y * BBB#))
        CCC# = BESSJ1(X) * Log(X) - 1# / X
        BESSY1 = X * AAA# / BBB# + 0.636619772 * CCC#
    Else
        Z = 8# / X
        Y# = Z ^ 2
        XX = X - 2.356194491
        AAA# = Sqr(0.636619772 / X)
        BBB# = P1 + Y * (P2 + Y * (P3 + Y * (P4 + Y * P5)))
        CCC# = Q1 + Y * (Q2 + Y * (Q3 + Y * (Q4 + Y * Q5)))
        BESSY1 = AAA# * (Sin(XX) * BBB# + Z * Cos(XX) * CCC#)
    End If
End Function