The National Library of Medicine classification system (NLM) uses the initial letters W and QS – QZ , which are not used by LCC. Some libraries use NLM in conjunction with LCC, eschewing LCC's R for Medicine. Others use LCC's QP – QR schedules and include Medicine R . [ clarification needed ]  
In the late 1890s, this classification began to be superseded by the Harvard classification, which is discussed in the remainder of this article.    The roman numerals used for Secchi classes should not be confused with the completely unrelated roman numerals used for Yerkes luminosity classes.
The 2010 Standard Occupational Classification (SOC) system is used by Federal statistical agencies to classify workers into occupational categories for the ...
The files are also available for downloading in WordPerfect format (noted as WP version) and in Word format (noted as Word version).