1. A method for measuring the renewable bio-content in renewable bioplastic resin during a production run comprising: a.) obtaining at least three resin samples during the production run, wherein each resin sample is obtained a different time point; b.) measuring δ 13 C values of the at least three resin samples; c.) determining the actual renewable bio-source carbon content of two of the at least three resin samples in step b.) with the lowest and the highest δ 13 C value; d.) determining the correlation between the two actual renewable bio-source carbon content determined in step c.) and the corresponding δ 13 C values of the two samples; e.) determining the renewable bio-source carbon content of the remaining resin sample(s) obtained in step a.) based on said correlation and the measured δ 13 C values of the remaining resin sample(s); and f.) calculating the renewable bio-content of the renewable bioplastic resin sample(s) from the renewable bio-source carbon content determined in step e.), wherein the production run occurs in a production facility transitioning from i) at least one non-renewable petroleum-derived monomer to at least one renewable bio-derived monomer; or ii) at least one renewable bio-derived monomer to at least one non-renewable petroleum-derived monomer.