As we have seen, various factors prevent the precise measurement of radiocarbon activity in a sample and, consequently, there is a statistical error or standard deviation (which may not have been realistically calculated) associated with all radiocarbon dates. Thus, when a radiocarbon date is quoted as 3700± 100 BP this means that there should be a 68 percent probability - two chances in three - that the correct estimate of age in radiocarbon years lies between 3800 and 3600 BP.