We studied the clarity of three requirements forms, operationalized as ease of problem detection, freedom from obstructions to understanding, and understandability by a variety of stakeholders.  A set of use cases for an industrial system was translated into ScenarioML scenarios and into sequence diagrams; problems identified during each translation were noted; and all three forms were presented to a range of system stakeholders, who were interviewed before and after performing tasks using the forms.  The data was analyzed, and convergent results were triangulated across data sources and methods.  The data indicated that ScenarioML scenarios best support requirements clarity, then sequence diagrams but only for stakeholders experienced with them, and finally use cases as the least clear form.