For both the gas proportional counter and liquid scintillation counter, what is measured is the number of beta particles detected in a given time period.
Radiocarbon dating is a method of what is known as absolute dating.
However, when an organism dies, it ceases to consume carbon.
More recently, has become the method of choice; it counts all the 14 C atoms in the sample and not just the few that happen to decay during the measurements; it can therefore be used with much smaller samples as small as individual plant seeds , and gives results much more quickly.
Maybe one in a trillion carbon atoms are carbon-14.
The curve showed two types of variation from the straight line: a long term fluctuation with a period of about 9,000 years, and a shorter-term variation, often referred to as "wiggles", with a period of decades.