Everything is arranged alphabetically by the country or international organization that published it. All call numbers have 3 elements, separated by spaces. The first two letters of the call number refer to the country or the international organization responsible for the publication. Other international organizations, such as OECD, Council of Europe, etc. For countries, the first 2 letters are followed by a number indicating the level of government.
Federal government is considered the first level.
United States Federal Government Provincial or state government is considered the second level of government. The second element of the call number, which is set off by a space, indicates the government department, or region, or city. The third and last element in the call number for a book or monograph gives information about the year of publication and the title of the book. It is set off from the second element of the call number by a space. HW refers to the Federal Dept. of Health.