A date in a calendar is a reference to a particular day represented within a calendar system. The calendar date allows the specific day to be identified. The number of days between two dates may be calculated. For example, " 24, 2018" is ten days after " 14, 2018" in the Gregorian calendar. The date of a particular event depends on the observed UTC offset. For example the attack on Pearl Harbor that began at 1941-12-07T18:18Z took place on December 7 according to Hawaii Time (UTC-10:30), and on December 8 according to Japan Standard Time (UTC+09).