anchor.diff:      opK1K2 = 'l'
   !   print *,"opK1K2 = ", opK1K2
     ENDIF
  -
  +  IF (PRESENT(optGAS)) THEN
  +    opGAS = optGAS
  +  ELSE
  +    opGAS = 'Pinsitu'
  +  ENDIF
   
     icount = 0
     DO i = 1, N
  
positive.code: !!    total alkalinity (ALK), dissolved inorganic carbon (DIC),
  !!    silica and phosphate concentrations (all 1-D arrays)
  SUBROUTINE vars(ph, pco2, fco2, co2, hco3, co3, OmegaA, OmegaC, BetaD, rhoSW, p, tempis,  &
                  temp, sal, alk, dic, sil, phos, Patm, depth, lat, N,                          &
                  optCON, optT, optP, optB, optK1K2, optKf                                  )
  
    !   Purpose:
    !     Computes other standard carbonate system variables (pH, CO2*, HCO3- and CO32-, OmegaA, OmegaC, R)
  
negative.code:   !> for K1,K2 choose either \b 'l' (Lueker et al., 2000) or \b 'm10' (Millero, 2010) 
  !f2py character*3 optional, intent(in) :: optK1K2='l'
    CHARACTER(3), OPTIONAL, INTENT(in) :: optK1K2
    !> for K0,fugacity coefficient choose either \b 'Ppot' (no pressure correction) or \b 'Pinsitu' (with pressure correction) 
    !! 'Ppot'    - for 'potential' fCO2 and pCO2 (water parcel brought adiabatically to the surface)
    !! 'Pinsitu' - for 'in situ' values of fCO2 and pCO2, accounting for pressure on K0 and Cf
    !! with 'Pinsitu' the fCO2 and pCO2 will be many times higher in the deep ocean
  !f2py character*7 optional, intent(in) :: optGAS='Pinsitu'
    CHARACTER(7), OPTIONAL, INTENT(in) :: optGAS
  
  ! Output variables:
    !> pH on the <b>total scale</b>
  