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

 tangent

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

    The tangent of the angle whose value (in degrees) is to be
    returned. The tangent argument is the address of a floating-point
    number that is this tangent. For MTH$ATAND, tangent specifies an
    F-floating number. For MTH$DATAND, tangent specifies a D-floating
    number. For MTH$GATAND, tangent specifies a G-floating number.