How the age of a tree can be estimated from the analysis of the rings present on a cross section of its stem?

For the growth of the tree it is essential to have formation of new vessels within the stem, a task performed by the vascular cambium. The vascular cambium is more dynamic in hot seasons (spring and summer) generating a lighter band made of large calibered vessels. During the winter and fall the vascular cambium produces the opposite, so small calibered vessels and a darker band appear outside the previous lighter band. Consequently two ring bands are made yearly, one lighter and the other darker. By a straight count of these band pairs one can estimate the age of the tree.