percent modern carbon
normalized and standardized value for the amount of the 14C isotope in a sample, calculated relative to the standardized and normalized 14C isotope amount of oxalic acid standard reference material, SRM 4990c SRM 4990c is an example of a suitable product supplied by the US National Institute of Standards and Technology. This information is given for the convenience of users of this document and does not constitute an endorsement by ISO of the product named. Equivalent products may be used if they can be shown to lead to the same results.