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Because the "present" time changes, standard practice is to use 1 January 1950 as commencement date of the age scale, reflecting the fact that radiocarbon dating became practical in the 1950s.The abbreviation "BP", with the same meaning, has also been interpreted both of which requested that publications should use the unit "a" for year and reserve the term "BP" for radiocarbon estimations. A large quantity of contemporary oxalic acid dihydrate was prepared as NBS Standard Reference Material (SRM) 4990B. This value is defined as "modern carbon" referenced to AD 1950.
Many scholarly/scientific journals require that published calibrated results be accompanied by the name (standard codes are used) of the laboratory concerned, and other information such as confidence levels, because of differences between the methods used by different laboratories and changes in calbrating methods.This has to do with the fact that the level of atmospheric radiocarbon (carbon-14 or C) has not been strictly constant during the span of time that can be radiocarbon-dated.Uncalibrated radiocarbon ages can be converted to calendar dates by means of calibration curves based on comparison of raw radiocarbon dates of samples independently dated by other methods, such as dendrochronology (dating on the basis of tree growth-rings) and stratigraphy (dating on the basis of sediment layers in mud or sedimentary rock).No, the same problem would have to be addressed in the coming years.To adjust for that, then, scholars now typically cite both raw, uncalibrated radiocarbon dates as years RCYBP (radiocarbon years before the present as 1950), alongside calibrated versions of those dates as cal BP, cal AD and cal BC (calibrated or calendar years BP, AD, and BC).