In the nineteenth century, bidders on a contract would develop a small-scale non-operational physical version of the final product. The bidder would keep changing the small physical model until stakeholders were satisfied. The contract for the ship would then reference this small-scale physical model. But for technologically complex projects, stakeholders needed more information about the functions the solution will form. In fact, committing to a particular physical shape too early could potentially prevent the design team from achieving all of the stakeholder requirements. As a result, detailed physical models were replaced with inexpensive mock-ups (often focused on getting feedback on user interfaces.) Mock-ups, like the physical models were incapable of performing any functions.