anchor.diff:  
               ! ! if the latter works, put this call at the end of current module
               ! if (use_delta_terrain) then
  -            call delta_terrain(this, terrain_u, terrain_v, dz_scl, max_level, H, options)
  +            call calculate_delta_terrain(this, terrain_u, terrain_v, dz_scl, max_level, H, options)
               !   ! if sleve then dz = dzscale (below max_level, above max_level dzdx = 0)
               !   ! else 
               ! endif
  
positive.code:           
          enddo 
  
          call io_write("zfr_u.nc", zfr_u, zfr_u(:,:,:) ) ! check in plot
          
          print *, "zfr_u min/max: ", min(zfr_u), " / ", max(zfr_u)
  
  
negative.code: 
  
  
      subroutine calculate_delta_terrain(this, terrain_u, terrain_v, dz_scl, max_level, H, options)
          implicit none
          class(domain_t),  intent(inout) :: this
          ! type(boundary_t), intent(inout) :: forcing
  