Radiocarbon calibration (original) (raw)

Radiocarbon dating measurements produce ages in "radiocarbon years", which must be converted to calendar ages by a process called calibration. Calibration is needed because the atmospheric 14C/12C ratio, which is a key element in calculating radiocarbon ages, has not been constant historically. The term Before Present (BP) is established for reporting dates derived from radiocarbon analysis, where "present" is 1950. Uncalibrated dates are stated as "uncal BP", and calibrated (corrected) dates as "cal BP". Used alone, the term BP is ambiguous.