anchor.diff:    REAL(kind=r8) :: t, tk, prb
     REAL(kind=r8) :: s, sqrts, s15, scl
   
  +  REAL(kind=r8) :: Phydro_atm, Patmd, Ptot, Rgas_atm, vbarCO2
  +
   ! Arrays to pass optional arguments into or use defaults (Dickson et al., 2007)
     CHARACTER(3) :: opB
     CHARACTER(2) :: opKf
  
positive.code: 
    !     INPUT variables:
    !     ================
    !     depth   = depth [m]     (with optP='m', i.e., for a z-coordinate model vertical grid is depth, not pressure)
    !             = pressure [db] (with optP='db')
    !     lat     = latitude [degrees] (needed to convert depth to pressure, i.e., when optP='m')
  
negative.code:         Kf(i) = Kf_0p * EXP(lnkpok0(6)) !Pressure correction (on Free scale)
          Kf(i) = Kf(i)/total2free        !Convert back from Free to Total scale
  
  !       Convert between seawater and total scales
          free2SWS  = 1.d0 + St(i)/Ks(i) + Ft(i)/(Kf(i)*total2free)  ! using Kf on free scale
          total2SWS = total2free * free2SWS                          ! KSWS = Ktotal*total2SWS
          SWS2total = 1.d0 / total2SWS
  