Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy.
Once the radiocarbon concentration in a sample has been measured, the sample's age in "radiocarbon years" is determined mathematically.
The radiocarbon age must then be calibrated to determine the sample's age in calendar years.
Radiocarbon dates are certainly not precise to within a year or two, but they are generally precise to within a few hundred years or better.
This means radiocarbon's precision is generally sufficient to choose between alternate chronologies which differ by a hundred years or more.
Thus it is possible in some instances for two samples from a few decades apart to have the same radiocarbon concentration today, and hence the same apparent radiocarbon age.
This happens whenever there is a wiggle in the curve at the time the samples died.Modern radiocarbon dating uses tree-ring chronologies to produce the calibration curve.Because the radiocarbon to stable carbon ratio in the atmosphere has fluctuated over time, there are "wiggles" in the calibration curve.After another 5,730 years only one-quarter of the original carbon-14 will remain.After yet another 5,730 years only one-eighth will be left.Coins found in excavations may have their production date written on them, or there may be written records describing the coin and when it was used, allowing the site to be associated with a particular calendar year.