Code 680 - Library of Congress ClassificationOptional, repeatable Indicators not definedSubfields: a - LCC Number - single or beginning of a range (NR) b - LCC Number - end of a range (NR) c - Explanatory terms (R)Code 686 - Other Classification NumbersOptional, repeatable Indicators not definedSubfields: a - Class number, single or beginning of a range (NR) b - Class number, end of a range (NR) c - Explanatory terms (R) 2 - Subject system code (NR)