A key year is a year in which a significant number of trees had a wider or narrower growth ring than the previous year. A non-key year is a year which there vas not a significant number of trees that had greater or less growth than the previous year. A key-year pattern is a series of key years that are separated in time by non-key years. Keyyear patterns have proven useful in determining the date of construction of buildings of historical significance (Heikkenen 1980). A white ash key-year pattern was constructed, using 4 radii from 3 tree heights of 16 trees. Radii from a tree height of 0.3. (1 ft) above ground were found to have higher agree.ent with the white ash key-year pattern than radii from positions higher in the tree. Long radii (from off-centered piths) were found to have higher agreement than the shorter radii. The long radii from lower heights had twice the level of agreement as the short radii at upper heights. The amount of agreement decreased as the number of trees used to construct the key-year pattern was dropped from 16 to 8. At least 8 samples of long radii from lower tree heights were needed to construct a key-year pattern. At least 12 samples were needed from short radii at upper tree heights to construct a key-year pattern. Twelve samples were sufficient to produce a key-year pattern, when sampling from unknown heights and radial lengths (i.e. log houses). / Master of Science