Dates determined using radiocarbon dating come as two kinds: uncalibrated (also called Libby or raw) and calibrated (also called Cambridge) dates. Such calibrated dates are expressed as cal BP, where cal indicates calibrated years, or calendar years, before 1950.

What is the difference between radiocarbon years and calibrated radiocarbon years?

Radiocarbon measurements are based on the assumption that atmospheric carbon-14 concentration has remained constant as it was in 1950 and that the half-life of carbon-14 is 5568 years. Calibration of radiocarbon results is needed to account for changes in the atmospheric concentration of carbon-14 over time.

Is BP the same as BC?

Dates can be expressed as AD, BC, BCE (before common era), and BP (before present). The accepted way to represent C-14 ages is in terms of years BP, where the year 1950 is used as the present. (1950 is the date that the calibration curves were established.