Since the data points have the same Y-value and a range of X-values, they initially fall on a horizontal line: half-lives will include zero within its range of uncertainty.

(The range of uncertainty varies, and may be as much as an order of magnitude different from the approximate value above.

Age "uncertainty" When a "simple" dating method is performed, the result is a single number.

There is no good way to tell how close the computed result is likely to be to the actual age.

The wonderful property of isochron methods is: if one of these requirements is violated, it is nearly certain that the data will indicate the problem by failure to plot on a line.

The "generic" method described by Gonick is easier to understand, but it does not handle such necessities as: (1) varying levels of uncertainty in the X- versus Y-measurements of the data; (2) computing an uncertainty in slope and Y-intercept from the data; and (3) testing whether the "fit" of the data to the line is good enough to imply that the isochron yields a valid age.

However, the methods must be used with care -- and one should be cautious about investing much confidence in the resulting age...

especially in absence of cross-checks by different methods, or if presented without sufficient information to judge the context in which it was obtained.

Each such age would match the result given by the isochron.

Gain or loss of In order to make the figures easy to read (and quick to draw), the examples in this paper include few data points.