Abstract
Smoothed curves are least-squares fitted to three sets of decadal radiocarbon calibration data from New Zealand and British Isles (AD 1725–1935) and western North America (AD 1145–1945). The curves are compared with each other and with a curve previously calculated from New Zealand data (AD 1335–1745). The smoothing procedure results in reduced standard deviations of the curves, but at the expense of time resolution. The comparison shows a variable 14C offset between the northern and southern hemispheres of 0–70 years (Southern Hemisphere older), and a Northern Hemisphere longitudinal variation of −20 to +60 years (British Isles generally older than western North America).