| Mandatory | Repeatable | Editable |
|---|---|---|
| no | may occur only once per ownership description | yes |
Indicates the reliability of the information given on a specific piece of evidence and the type of source from which it has been gained.
The evidence sequence number in $6 groups all chunks of information that describe the evidence for a specific ownership. All fields with an identical subfield $6 within a record describe the same ownership.
$a is a coded subfield with exact one code position:
| a | The recording of this piece of evidence is considered certain. |
| b | The recording of this piece of evidence is considered uncertain. |
$b is a coded subfield with up to 6 code positions. The code positions are filled from left to right, any unused code position is left empty.
| a | Book in Hand |
| b | Bibliography |
| c | Library Catalogue |
| e | Auction/Sales Catalogue |
| f | Hist. Library Catalogue / Accession Journal |
| x | unknown/other |