066 Subfield $a - Primary G0 character set:

Subfield $a contains a code identifying the primary character set. The code is the Intermediate and Final characters of the escape sequence that designates and invokes the default G0 character set. Since MARC Latin (including ASCII, MARC Greek, MARC subscript, or MARC superscript) is the MARC default set, if it is the primary set it does not need to be identified in this subfield.

Examples:

066 ##$a(N

[The Intermediate character in the designation sequence is hex 28 (ASCII graphic "(") that identifies the character set as one byte per character and its use as a G0 set, and the Final character is hex 4E (ASCII graphic "N") that identifies the Basic Cyrillic character set.]

066 ##$a$1

[The Intermediate character in the designation sequence is hex 24 (ASCII graphic "$") that identifies the character set as multiple bytes per character and its use as a G0 set, and the Final character is hex 31 (ASCII graphic "1") that identifies the Chinese, Japanese, Korean character set.]