然而，使用BP的一个主要缺点是，今年当然每12个月就会发生变化。如果这是一个简单的向后计算问题，那么今天在50年内准确测量和发布的500 BP将是550 BP。我们需要一个固定的时间点作为起点，以便所有BP日期无论何时发布都是等效的。由于BP指定最初与放射性碳测年相关，考古学家选择1950年作为“现在”的参考点。选择那个日期是因为放射性碳测年是在20世纪40年代后期发明的。与此同时，大气层核试验在1940年代开始向大气层投入大量碳。 1950年以后的放射性碳日期实际上是无用的，除非我们能够找到一种方法来校准仍然沉积在我们大气中的过量碳。尽管如此，1950年是很久以前的 – 我们应该将起点调整到2000年吗？不，在未来几年内必须再次解决同样的问题。学者们现在通常将原始的，未校准的放射性碳年代称为RCYBP年（1950年之前的放射性碳年），以及那些日期的校准版本，如校准BP，校准AD和校准BC（校准或日历年BP，AD和BC） 。这可能看起来似乎过分，但过去有一个稳定的起点来连接我们的日期总是有用的，尽管我们现代的，多元文化共享的日历已经过时的宗教基础。所以，当你看到2000 cal BP时，想想“1950年以前的2000年”或者计算到公元前50年的年份。无论何时发布，它总是意味着。
加拿大女王大学考古学论文代写：准确测量和发布
However, one of the main drawbacks of using BP is that this year, of course, changes every 12 months. If this is a simple backwards calculation problem, the 500 BP that is accurately measured and released today in 50 years will be 550 BP. We need a fixed point in time as a starting point so that all BP dates are equivalent whenever they are published. Since the BP designation was originally associated with radiocarbon dating, archaeologists chose 1950 as the “now” reference point. The date was chosen because the radiocarbon dating was invented in the late 1940s. At the same time, the atmospheric nuclear test began to invest large amounts of carbon into the atmosphere in the 1940s. The radiocarbon date after 1950 is virtually useless unless we can find a way to calibrate excess carbon still deposited in our atmosphere. Still, 1950 was a long time ago – should we adjust the starting point to 2000? No, the same problem must be solved again in the next few years. Scholars now usually refer to the original, uncalibrated radiocarbon ages as RCYBP years (radiocarbon years before 1950), as well as calibration versions of those dates, such as calibration BP, calibration AD, and calibration BC (calibration or calendar year BP) , AD and BC). This may seem excessive, but it has always been useful to have a stable starting point to connect our dates, even though our modern, multicultural shared calendar has an outdated religious foundation. So, when you see 2000 cal BP, think about “2000 before 1950” or calculate the year to 50 BC. Whenever it is released, it always means.