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. Since the calendar age of the tree rings is known, this then tells you the age of your sample.

What dating technique was used to calibrate or correct dates from the radiocarbon dating?

Tree rings Tree rings are used to calibrate radiocarbon measurements. Calibration is necessary to account for changes in the global radiocarbon concentration over time.