1. This rule is for calculating the content of casks or barrels and associated tasks.

2. This rule has scales on two faces which was a feature of the earlier versions of Everard's rule and the other hand it has a "folded" D scale (i.e. the scale has values ro root 10 on the upper part of the stock and value from root 10 to 10 on the lower part.

3. For more information on this type of rule see here.