Suppose a requirement is "The automated interfaces of the system must be easy to learn". There is no obvious measurement scale for "easy to learn". However if we investigate the meaning of the requirement within the particular context, we can set communicable limits for measuring the requirement.
Again we can make use of the question: "What is considered a failure to meet this requirement?" Perhaps the stakeholders agree that there will often be novice users, and the stakeholders want novices to be productive within half an hour. We can define the quality measure to say "a novice user must be able to learn to successfully complete a customer order transaction within 30 minutes of first using the system". This becomes a quality measure provided a group of experts within this context is able to test whether the solution does or does not meet the requirement.
An attempt to define the quality measure for a requirement helps to rationalise fuzzy requirements. Something like "the system must provide good value" is an example of a requirement that everyone would agree with, but each person has his own meaning. By investigating the scale that must be used to measure "good value" we identify the diverse meanings.