The purpose of this paper is to emphasize the precision of the dating of individual rings in long tree-ring chronologies by the use of methods and procedures classed under the name 'dendrochronology'. The operations are based on climatic impressions upon the individual rings or trees-trees so located that climatic changes from year to year are of highest importance to the individual tree. The climatic source of these impressions is identified by the faithful agreement between many trees, in the resulting ring patterns year by year, through the active lives of contemporary trees as will be shown below; thence this tree-ring chrononlogy is extended back nearly 2,000 years in the Southwest by the overlapping lives of generations of trees. Archaeological dating, whose results have been more generally published, sometimes follows this precision dating very closely. But in most cases, one, two, or three corrections are needed, usually very small but rarely strictly precise: (a) for crowded and unreadable outside rings; (b) for definite loss of outside rings; and (c) for lapse of time from death of thee tree to its actual use in house construction or for other purpose. The actual extension of this dating back through the centuries has depended strongly on the archaeologists who generously supplied the specimens. So the name dendrochronology has been associated with their work.