The Conventional Radiocarbon Age BP is calculated using the radiocarbon decay equation: Where -8033 represents the mean lifetime of 14C (Stuiver and Polach, 1977).
Amongst accelerator laboratories there has been mooted the theoretical possibility of extended range dating to 75 000 yr , at present this seems difficult to attain because of the problems in accurately differentiating between ions that mimic the mass and charge characteristics of the C14 atom.
The terms "%Modern", or "pm C" and D14C are shown related in this diagram along with the Radiocarbon age in years BP (Before 1950 AD).
If the reservoir corrected conventional radiocarbon age calculated is within the past 200 years, it should by convention be termed 'Modern' (Stuiver and Polach, 192).
Ninety-five percent of the activity of Oxalic Acid from the year 1950 is equal to the measured activity of the absolute radiocarbon standard which is 1890 wood.
This is the International Radiocarbon Dating Standard.