Graph of radiocarbon dating accuracy
The output is along the bottom axis; it is a trimodal graph, with peaks at around 710 AD, 740 AD, and 760 AD.Again, the ranges within the 1σ confidence range are in dark grey, and the ranges within the 2σ confidence range are in light grey.
There are separate graphs for the southern hemisphere and for calibration of marine data.
To produce a curve that can be used to relate calendar years to radiocarbon years, a sequence of securely dated samples is needed which can be tested to determine their radiocarbon age.
A third possibility is that the curve is flat for some range of calendar dates; in this case, illustrated by t The method of deriving a calendar year range described above depends solely on the position of the intercepts on the graph.
These are taken to be the boundaries of the 68% confidence range, or one standard deviation.
The study of tree rings led to the first such sequence: tree rings from individual pieces of wood show characteristic sequences of rings that vary in thickness because of environmental factors such as the amount of rainfall in a given year.
These factors affect all trees in an area, so examining tree-ring sequences from old wood allows the identification of overlapping sequences.
Programs to perform these calculations include Ox Cal and CALIB.
These can be accessed online; they allow the user to enter a date range at one standard deviation confidence for the radiocarbon ages, select a calibration curve, and produce probabilistic output both as tabular data and in graphical form.
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.
Suess said he drew the line showing the wiggles by "cosmic schwung" – freehand, in other words.
Where the curve varies significantly both up and down, a single radiocarbon date range may produce two or more separate calendar year ranges.