Once the radiocarbon concentration in a sample has been measured, the sample's age in "radiocarbon years" is determined mathematically.The radiocarbon age must then be calibrated to determine the sample's age in calendar years.Measurements can be made with a high degree of precision. Aardsma submitted a sample from a reed mat known to be over 5,000 years old.
Since Nitrogen gas makes up about 78 percent of the Earth's air, by volume, a considerable amount of Carbon-14 is produced.
The carbon-14 atoms combine with oxygen to form carbon dioxide, which plants absorb naturally and incorporate into plant fibers by photosynthesis.
There are several things that you might want to check for.
Fortunately for you, there's a spreadsheet that I (Becky) have written which does these things.
Some examples of the types of material that radiocarbon can determine the ages of are wood, charcoal, marine and freshwater shell, bone and antler, and peat and organic-bearing sediments.
Age determinations can also be obtained from carbonate deposits such as calcite, dissolved carbon dioxide, and carbonates in ocean, lake, and groundwater sources.Thus it is possible in some instances for two samples from a few decades apart to have the same radiocarbon concentration today, and hence the same apparent radiocarbon age.This happens whenever there is a wiggle in the curve at the time the samples died.The precision of a radiocarbon date tells how narrow the range of dates is.There are two main factors which determine the precision of a radiocarbon date.Animals and people take in carbon-14 by eating the plants.The ratio of normal carbon (carbon-12) to carbon-14 in the air and in all living things at any given time is nearly constant.A common misconception about radiocarbon dating is that it gives a precise date---3577 B. In actual practice radiocarbon dating can only give a range of dates for a given sample---3650 to 3410 B.C., for example---the true date lying somewhere in that range.This, in fact, is the most significant factor contributing to loss of precision in radiocarbon dates today.However, this contribution is usually only a few decades.