There are three methods that can be used to determine the age of a sample tree at breast height: fell the tree at breast height and count rings on the stem cross-section, count rings on an increment core taken at breast height, and count annual branch whorls above breast height. These three methods of determining age differ in accuracy. Generally, it is easiest to get an accurate age by felling the tree and counting rings on the cut face. The method of counting branch whorls is the most difficult method to use to get an accurate age. Counting rings on an increment core is intermediate in difficulty.
Rings are easiest to count on high quality cores. To obtain high quality cores, keep your increment borer sharp and clean. Hold the borer steady when you begin to drill. Re-drill the tree until you get an increment core that contains the pith. Often you can improve your chances of hitting the pith by aligning the borer with tree center using the branch angles into the pith.