Prototype Build a throwaway prototype at the fidelity that can answer this question, before committing an approach later work will treat as given. Then apply the decisions or hand off. Do not fake the dimension being tested. Modality, fidelity, and medium all follow from that one rule. A question about how a flow or state model behaves is settled by driving it, so a screen that only looks like the product does not answer it. A question about how a layout or a mark reads is settled by seeing it at real finish, so a thin sketch does not answer it either. The user's own perception settles the qu…