No, you misunderstood. It means you have two systems, Old and New. You use Old and start development of New. And you do the payroll on both, and if there's a di

No, you misunderstood. It means you have two systems, Old and New. You use Old and start development of New. And you do the payroll on both, and if there's a difference you debug that and modify New. After a while it's good enough. And you stop using Old.