The wood in these rings once laid down remains unchanged during the life of the tree.
This is very useful as a record of the radiocarbon concentration in the past.
The results of calibration are often given as an age range.
In this case, we might say that we could be 95% sure that the sample comes from between 1375 cal BC and 1129 cal BC.
Radiocarbon measurements are always reported in terms of years `before present' (BP).