Leader

• Positions 00–04
• Five-character number equal to the length of the entire record, including itself and the record terminator
• Right justified with leading zeros

• Position 05
• One-character alphabetic code that indicates the relationship of the record to a file for file maintenance purposes

• Position 06
• In bibliographic records, a one-character alphabetic code that differentiates records created for various types of content and materials
• In authority records, a one-character alphabetic code that indicates the characteristics of and defines the components of the record

• Position 07
• One-character alphabetic code that indicates the relationship between the item being cataloged and its constituent parts
• Bibliographic Level not defined in MARC 21 for authority records
• In those records, character position 07 contains a blank ()

• Position 08
• One-character code that indicates the archival control status
• Type of Control not defined in MARC 21 for authority records
• In those records, character position 08 contains a blank ()

• Position 09
• One-character code that identifies the Character Coding Scheme used in a record
• The coding scheme used affects the number of octets needed per character, the placement of non-spacing characters, and the use of escape sequences and may affect the character repertoire
• Character Coding Scheme not defined for authority records
• In OCLC records, character position 09 usually contains a blank ()
   Note: In records with the Unicode UTF-8 character set, leader position 09 is coded a.

• Position 10
• One-character number equal to the number of indicators occurring in each variable data field
• Two character positions at the beginning of each variable data field are reserved for indicators
• In OCLC records, always = 2

• Position 11
• One-character number equal to the number of character positions used for a subfield code in variable data fields
• A subfield code consists of a delimiter (‡) and a lowercase alphabetic or numeric data element identifier
• In OCLC records, always = 2

• Positions 12–16
• Five-character number that specifies the first character position of the first variable control field in the record
• The number is the base from which the starting character position of all the other fields in the record is addressed in the directory
• The starting character position in the directory entry for each field of the record is relative to the first character of the first variable control field rather than the beginning of the record
• Equal to the sum of the lengths of the leader and the directory, including the field terminator character at the end of the directory
• Right justified with leading zeros

• Position 17
• In bibliographic records, a one-character alphanumeric code that indicates the fullness of the bibliographic information and/or content designation
• In authority records, a one-character alphanumeric code that indicates whether the record is complete or incomplete  

• Position 18
• One-character alphanumeric code that indicates characteristics of the descriptive data in the record through reference to cataloging norms
• Descriptive Cataloging Form not defined for authority records
• In those records, character position 18 contains a blank ()

• Position 19
• One-character alphanumeric code that indicates whether a note containing basic identification information can be generated from a 76x–78x (Linking Entry) field without accessing the actual related record
• Linked Record Requirement not defined for authority records
• In OCLC records, character position 19 contains a blank ()

• Positions 20–23
• One-character number in each position that indicates the structure of the entries in the directory

• Length of Length-of-Field Portion

• Position 20
• One-character number that indicates the length-of-field portion of a directory entry
• In OCLC records, always = 4

• Length of Starting-Character-Position Portion

• Position 21
• One-character number that indicates the starting-character- position portion of a directory entry
• In OCLC records, always = 5

• Transaction Type Code/Length of Implementation-Defined Portion

• Position 22
• In bibliographic records, may contain either information coded in hexadecimal or a one-character code that indicates the transaction type code. (Transaction codes were stored in byte 22 prior to November 12, 2006.)

 Note: Since November 12, 2006, transaction codes for bibliographic records are stored in field 994. For historical details and a complete list of transaction codes, see the information on field 994 in chapter 2 of "Content Designators for Bibliographic Data."

• Non definito

• Position 23
• Non definito
• In OCLC records, always = 0