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This correction is performed as follows: $$Fm_ = Fm_ ( Fm_ - Fm_b)\frac$$ Where $$M$$ is sample mass, and $$M_b$$ and $$Fm_b$$ are the mass and Fm of the blank.Fraction Modern is a measurement of the deviation of the C is also affected by natural isotopic fractionation.After acceleration and removal of electrons, the emerging positive ions are magnetically separated by mass and the C counts per second are collected.

Since atmospheric carbon 14 arises at about the same rate that the atom decays, the Earth's levels of carbon 14 have remained constant.Therefore a 1% error in fraction-modern leads to an 80 year error in the age.Ages are rounded according to the convention of Stuiver & Polach, shown below.Due to variability in sample homogeneity, sample collection, and sample processing, the variability of replicate samples (reproducibility) is generally greater than the reported error for a single sample.A total measurement error can be estimated by adding in quadrature the reported error with this extra variability, or added variance.

Fractionation must be corrected for in order to make use of radiocarbon measurements as a chronometric tool for all parts of the biosphere.