As trees grow they produce annual rings of their growth which relate to the climate and nutrients they received in the growing season. A tree will store this information in its wood. Even if it is cut down this pattern, like a bar code, will be retained for the period of growing. Comparison of several trees growing in the same area at the same time will produce a similar, but not identical, pattern or dendrochronology. If a sequence of 50 tree-rings can be matched to a master sequence of all the growing seasons, then a date for a timber can sometimes be established.