A general meaning of this term is the most important items. When a group of products is analysed according to some criterion and the individual products in the group ranked - ie placed in order - according to the criterion used, it is common to subdivide the products in the ordered list into three categories. The "A" category, or A Class, products are those products at the top of the list; the "B" category products are next, and the "C" category products are those at the bottom of the list. A common criterion applied in the analysis of the original group of products is according to each product's "annual value". Annual value is often thought of as reflecting a product's importance, and is defined as the product's annual usage multiplied by its unit value. (For example, if 200 products are used per annum and one unit costs £7, the annual value is £1,400.) It will typically be found that if the A Class items are defined as the top 20% of the items at the top, that they account for 80% of the total value of all the items.