516. Exceptional cases.

516.     Exceptional cases.

The courts are not anxious to find insufficiency, if the specification is fairly drawn1, and will not do so merely because exceptional cases2 or unlikely materials3 might come within the words of the specification and will not work, or because the words do not exclude a mistake which a competent workman would not make4. The courts are also reluctant to find insufficiency on the ground that a claim purports to define its extent by reference to a qualitative rather than a quantitative requirement5. The question whether the directions