One system classifies coal by the content of volatile matter: with 10% volatile, anthracite; between 10% and 13% lean coal, semianthracite or dry-steam coal; 14% to 20%, variously designated; 20% to 30%, fat or coking coal. Other systems classify by calorific value, and caking and/or coking property. Post-World War II classifications include (1) volatile matter, (2) caking properties on rapid heating, and (3) coking properties.