anchor.diff:      call evaluate_zeta(zeta,uhalf,vhalf,nx,ny,layers,dx,dy)
   
   !    Now calculate d/dt of u,v,h and store as dhdtold, dudtold and dvdtold
  -    call evaluate_dhdt(dhdtold, hhalf,uhalf,vhalf,ah,dx,dy,nx,ny,layers, spongeHTimeScale,spongeH,wetmask)
  +    call evaluate_dhdt(dhdtold, hhalf,uhalf,vhalf,ah,dx,dy,nx,ny,layers, spongeHTimeScale,spongeH,wetmask,RedGrav)
       call evaluate_dudt(dudtold, hhalf,uhalf,vhalf,b,zeta,wind_x,&
           fu, au,ar,slip,dx,dy,hfacN,hfacS,nx,ny,layers,rho0,&
           spongeUTimeScale,spongeU,RedGrav,botDrag)
  
positive.code: !>
  !>     @section Overview
  !>     This model is an isopycnal model on an Arakawa C-grid with n
  !>     layers and a rigid lid.
  !>
  !>
  !>            
  
negative.code:     call evaluate_zeta(zeta,uhalf,vhalf,nx,ny,layers,dx,dy)
  
  !    Now calculate d/dt of u,v,h and store as dhdtveryold, dudtveryold and dvdtveryold
      call evaluate_dhdt(dhdtveryold, hhalf,uhalf,vhalf,ah,dx,dy,nx,ny,layers, spongeHTimeScale,spongeH,wetmask,RedGrav)
  
      call evaluate_dudt(dudtveryold, hhalf,uhalf,vhalf,b,zeta, &
          wind_x,fu, au,ar,slip,dx,dy,hfacN,hfacS,nx,ny,layers,rho0, &
  