6 Prototypes, Experiments, and Validation
6.1 Prototypes answer questions
A prototype need not resemble the final product. A cardboard mockup may test ergonomics; a breadboard may test a circuit; a software model may test logic; a subsystem rig may reveal vibration or thermal behavior.
6.2 Verification versus validation
Verification: Did the implementation meet the stated technical requirements? Validation: Does the resulting product solve the intended stakeholder problem in its actual context?
A prototype can pass every bench test and still fail validation because the team defined the wrong need.
6.3 Plan the test before building it
Document the purpose, configuration, instrumentation, acceptance criterion, number of trials, and failure handling. Avoid changing the pass criterion after seeing the result.
Example: If a design requirement states the system must keep water flow within \(\pm5\%\) of target over a specified interval, plan how many measurements and what calibration procedure will support that claim.
Task: Write a one-page test plan for one of your highest-risk requirements.
Living chapter. This is an initial working treatment. Derivations, examples, and references will be expanded in future editions.