      program gfs ! BB May 12 2017.
c Gravitational frequency shift due to h=5320 [ft].
      implicit real*8 (a-h,o-z)
c Speed of light in [m/s], feet [ft] in [m], g in [m/s^2]:
      parameter(iuo=6,c=3.d08,ft=0.3d00,g=9.8d00)
c Year in [s], height difference h [m]:
      parameter(y=365.d0*24.d0*3600.d0)
      h=5320*ft
      write(iuo,'(/," h,g =",2f9.2,/)') h,g
      dPhi=g*h
      rdf=exp(dPhi/c**2)-1.d00
      rdf1=dPhi/c**2 ! first order Taylor expansion of exp(dPhi/c^2).
      write(iuo,'(" ratio df/f =",1g13.5)') rdf
      write(iuo,'(" 1. order   =",1g13.5,/)') rdf1
      dt=rdf*y
      write(iuo,'(" Time difference over one year =",1g13.5)') dt
      dt=1.d06*dt
      write(iuo,'(" In microseconds               =",1f5.1,/)') dt
c
      h=160.0d03 ! m
      write(iuo,'(/," 2. h,g =",2f9.2,/)') h,g
      dPhi=g*h
      rdf=exp(dPhi/c**2)-1.d00
      rdf1=dPhi/c**2 ! first order Taylor expansion of exp(dPhi/c^2).
      write(iuo,'(" ratio df/f =",1g13.5)') rdf
      write(iuo,'(" 1. order   =",1g13.5,/)') rdf1
c
      stop "gfs: all done."
      end