Range of radiocarbon dating
Older samples have a lower concentration of radiocarbon, but they can be (and often are) counted for longer periods of time to compensate for this lower concentration.
By counting longer, the counting uncertainty in a radiocarbon measurement on a very old sample can be the same as that on a young sample.
Once the radiocarbon concentration in a sample has been measured, the sample's age in "radiocarbon years" is determined mathematically.
C., for example---the true date lying somewhere in that range.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.Measurements can be made with a high degree of precision. Aardsma submitted a sample from a reed mat known to be over 5,000 years old.The measurement, before calibration, came back with an error bar of /- about 60 radiocarbon years. It should be noted that these measurement uncertainties do not increase linearly as one goes back in time.