648 - Subject Added Entry-Chronological Term (R)

Indicators 1st -  Type of date or time period
  # No information provided
  0 Date or time period covered or depicted
  1 Date or time period of creation or origin
Subfields _a  Chronological term (NR)
  _v Form subdivision (R)
  _x General subdivision (R)
  _y Chronological subdivision (R)
  _z Geographic subdivision (R)
Examples
648 17 _a1860-1865_2fast
648 10 _aNineteenth century.
648 10 _aMiddle Ages.
648 10 _aNineteen forties.
648 #7 _a1900-1999_2fast