Scientists have also attempted to extend the calibration range by comparing results to timber which has its age calculated by [[dendrochronology]], but this has also been questioned because carbon dating is used to assist with working out dendrochronological ages. | Scientists have also attempted to extend the calibration range by comparing results to timber which has its age calculated by [[dendrochronology]], but this has also been questioned because carbon dating is used to assist with working out dendrochronological ages. |