In the BC/AD timeline, the year zero is omitted. History proceeds from December 31, 1 BC to January 1, 1 AD. This can lead to counting errors when summing up spans of time that cross the transition point, because people often assume the timeline is constructed like the set of integers. | In the BC/AD timeline, the year zero is omitted. History proceeds from December 31, 1 BC to January 1, 1 AD. This can lead to counting errors when summing up spans of time that cross the transition point, because people often assume the timeline is constructed like the set of integers. |