Function BESSK1(X)
    P1 = 1#:               P2 = 0.15443144
    P3 = -0.67278579:      P4 = -0.18156897
    P5 = -0.01919402:      P6 = -0.00110404
    P7 = -0.00004686
    Q1 = 1.25331414:       Q2 = 0.23498619
    Q3 = -0.0365562:       Q4 = 0.01504268
    Q5 = -0.00780353:      Q6 = 0.00325614
    Q7 = -0.00068245
    If X <= 2# Then
        Y# = X * X / 4#
        AAA# = Log(X / 2#) * BESSI1(X)
        CCC# = Y * (P5 + Y * (P6 + Y * P7))
        BBB# = P1 + Y * (P2 + Y * (P3 + Y * (P4 + CCC#)))
        BESSK1 = AAA# + (1# / X) * BBB#
    Else
        Y = (2# / X)
        BBB# = Y * (Q5 + Y * (Q6 + Y * Q7))
        AAA# = Q1 + Y * (Q2 + Y * (Q3 + Y * (Q4 + BBB#)))
        BESSK1 = (Exp(-X) / Sqr(X)) * AAA#
    End If
End Function