Calculating ΔR from a radiocarbon dated marine / terrestrial pair involves 3 steps:

1. Calibrate the terrestrial date with the northern hemisphere calibration curve
2. Reverse-calibrate discrete points on the resulting probability density function (PDF) with the marine calibration curve
3. Use a convolution integral to determine a confidence interval for the offset between the radiocarbon dated marine sample and the reverse-calibrated PDF of the atmospheric sample.

The resulting confidence interval will generally not be normally distributed. However, the result will be approximated as a normal distribution.