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

    OpenVMS usage:floating_point
    type:         F_floating, D_floating, G_floating
    access:       write only
    mechanism:    by value

    Angle in degrees. MTH$ATAND returns an F-floating number.
    MTH$DATAND returns a D-floating number. MTH$GATAND returns a
    G-floating number.