051 Subfield $a - Classification number:

Subfield $a contains the classification number. The instructions for recording subfield $a are the same as for field 050 (Library of Congress Call Number) . Subfield $a must always be present.

Example:

050 00$aQE75$b.P9 subser.

051 ##$aQE75$b.G4$c2d set.

051 ##$aMicrofilm$b3741 HV$cMicrofilm.

[A microfilm shelf number for a book.]