During the first half of the 20th century, the astronomer A. Douglass founded the Laboratory of Tree-Ring Research at the University of Arizona.
However, we can look for certain years that offer good "signals" (very thin or very wide rings) and identify them in each core and confirm they occur at the year they should in each core.
The skeleton plot is the tool used to discover these "signal years" and subsequently cross-validate each core for exact dates.
Please consult Field Methods for a detailed description of the field equipment, including its use and care, and the actual methods of core collection and preservation. The cores should next be mounted and glued in to increment core holders and then the surface prepared for study following the protocols outlined in Lab Methods.
Following surface preparation, you can begin the process of crossdating.
For each core that we have, we need to gain a high confidence in the actual date that we assign to each ring.
Unfortunately, any given tree may sometimes have a missing ring or a false ring present and therefore every ring we count thereafter is thrown off by one or two years.
The danger in attempting to date samples with relatively few rings, regardless of how the data are treated, is emphasized by these results.
Even in relatively straightforward cases, all methods employed are sometimes found to produce spurious dates or to fail to identify a known correct match.
Since cross-dating depends on matching the high-frequency elements of a sample against a master chronology, various methods are explored for removing the low-frequency variance in ring-width series before they are compared.
The results show that a range of such “pre-whitening” methods can usefully be employed, and no single method is universally superior.
These data should be entered in to an Excel (or equivalent) spreadsheet for subsequent analysis.