When there is a concern that a tree's non visible interior structure may be compromised, we use a variety of tools and knowledge to measure the soundness of the internal wood tissue. One such tool is the Resistograph that uses a micro drill bit to measure, and simultaneously graph out the density of the wood tissue as it penetrates the tree. Its sensitivity is such that it can pick up the difference between the density of spring and summer wood tissue, otherwise known as the annual ring.

Above: Steve Sprickman using a resistograph to check out an old pruing wound
Below: John Traverso shows us the Resistograph in action.