A metric for a specific feature should always fall within the defined specifications; otherwise the documentation is meaningless and must be changed accordingly. Certain metrics can most likely have only a lower or upper limit if the design calls for it, such as a coating having a curing time of at least 2 hours where any time spent curing after 2 hours does not affect the coatings function in anyway, this would also have to be verified beforehand. The physical limitations of the materials also play a crucial role in limiting their design specification and the specifications of other parts. If a part needs to be made from a specific polymer that cannot be subject to temperatures above a certain threshold that the entire device is affected if temperature is a factor in its function.