Once a sample is skeleton plotted, the plot is compared to an existing dated master chronology to match its pattern of marks in mirror image and thus find the exact years of formation of all rings. &nbsp; For example, the dated master chronology above is constructed from previously crossdated samples, it extends from 1885 to 1973, and it has a time series of standardized growth indices that average 1.0 and that range from 0.0 (very little growth) to 2.0 (maximum growth). &nbsp; <IMG SRC="chronology.gif"> The master is also marked as if it were a skeleton plot, with small indices represented by long marks and large indices represented by "b" marks. &nbsp; (For a good idea of how to make marks when skeleton plotting, look at the master chronology to see what values of ring growth merit a long mark versus no mark at all versus a "b" mark).