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).
Standard errors released with each radiocarbon assay (see below) are usually rounded by convention (Stuiver and Polach, 1977).
Again, not all laboratories subscibe to these conventions, some do not round up ages.
The Conventional Radiocarbon Age BP is calculated using the radiocarbon decay equation: Where -8033 represents the mean lifetime of 14C (Stuiver and Polach, 1977).