The better the fit of the data to the line, the lower the uncertainty.

Isochron methods avoid the problems which can potentially result from both of the above assumptions.

Isochron dating requires a fourth measurement to be taken, which is the amount of a different isotope of the same element as the daughter product of radioactive decay.

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 simplest form of isotopic age computation involves substituting three measurements into an equation of four variables, and solving for the fourth.

The equation is the one which describes radioactive decay: If one of these assumptions has been violated, the simple computation above yields an incorrect age.

Whether there's a data point on the Y-axis or not, the Y-intercept of the line doesn't change as the slope of the isochron line does (as shown in Figure 5).

Therefore, the Y-intercept of the isochron line gives the initial global ratio of could be subtracted out of each sample, and it would then be possible to derive a simple age (by the equation introduced in the first section of this document) for each sample.

Unfortunately, one must wade through some hefty math in order to understand the procedures used to fit isochron lines to data.