Radiocarbon dating dendrochronology
Once calibrated a radiocarbon date should be expressed in terms of cal BC, cal AD or cal BP.
The cal prefix indicates that the dates are the result of radiocarbon calibration using tree ring data.
The pair of blue curves show the radiocarbon measurements on the tree rings (plus and minus one standard deviation) and the red curve on the left indicates the radiocarbon concentration in the sample.
The grey histogram shows possible ages for the sample (the higher the histogram the more likely that age is).
These are the basis for the calibrations performed by the programs like CALIB and Ox Cal. Calibration of radiocarbon determinations is in principle very simple.
If you have a radiocarbon measurement on a sample, you can try to find a tree ring with the same proportion of radiocarbon.
By using these widths, it is possible to compare the tree rings in a dead tree to those in a tree that is still growing in the same region.between 2940BP and 3060BP for the measurement 3000 -30BP).A slightly different method is now more often used which is called the `probability method'.These values should correspond exactly to normal historical years BC and AD.The term cal BP means the number of years before 1950 and can be directly compared to calendar years.