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The following short FORTRAN program reproduces the critical table for
refraction from the NA.  It is NOT based on fitted equations.  It uses
the canonical multilayer-ray-following method of Biot-Auber-Standish
(Astronomical Journal,119,2472-2474,2000 May).  It calls the slREFRO
program of Wallace based on the work of Hohenkerk (HMNAO. Sept 1984).
http://stsdas.stsci.edu/cgi-bin/gethelp.cgi?refro.hlp
You can change pressue, temp, humidity, etc to generate your own
table.

    program dwrefracna
    implicit none
    real*8 ZOBS,HM,TDK,PMB,RH,WL,PHI,TLR,EPS,REF
    real*8 pi,xi,rlim
    print*,'from dwrefracna.f'
    pi=4.d0*datan(1.d0)
    print*,pi
    hm=0.d0
    phi=45.d0*pi/180.d0
c na 2007 values
    tdk=273.15d0+10.d0
    pmb=1010.d0
    rh=0.80d0
    wl=0.50169d0
c assume tlr .0065
    tlr=0.0065d0
    eps=1d-10
    rlim=+5.35d0
    do 4 xi=9.d0,90.d0,1.d0/60.d0
    zobs=pi/180.d0*(90.d0-xi)
    call slRFRO(ZOBS,HM,TDK,PMB,RH,WL,PHI,TLR,EPS,REF)
    ref=ref*180.d0/pi*60.d0
    if(ref.lt.rlim)then
        print'(i3,f4.0,f8.5)',int(xi-1.d0/60.d0)
     &       ,60.d0*(xi-1.d0/60.d0-int(xi-1.d0/60.d0))
        print'(8x,a1,f3.1)','-',rlim
        rlim=rlim-.1d0
    endif
4   continue
    end


 from dwrefracna.f
  3.14159265
  9 55.
        -5.3
 10  7.
        -5.2
 10 20.
        -5.2
 10 32.
        -5.1
 10 46.
        -5.0
 10 59.
        -4.9
 11 14.
        -4.8
 11 29.
        -4.7
 11 44.
        -4.6
 12  0.
        -4.5
 12 17.
        -4.4
 12 35.
        -4.3
 12 53.
        -4.2
 13 12.
        -4.1
 13 32.
        -4.0
 13 53.
        -3.9
 14 16.
        -3.8
 14 39.
        -3.7
 15  3.
        -3.6
 15 29.
        -3.5

etc.


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