VMS Help RTL Routines, MTH$, MTH$xTAN, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 angle-in-radians

    OpenVMS usage:floating_point
    type:         F_floating, D_floating, G_floating
    access:       read only
    mechanism:    by reference

    The input angle (in radians). The angle-in-radians argument is
    the address of a floating-point number that is this angle. For
    MTH$TAN, angle-in-radians specifies an F-floating number. For
    MTH$DTAN, angle-in-radians specifies a D-floating number. For
    MTH$GTAN, angle-in-radians specifies a G-floating number.