The Resistograph is a device used to identify and access the extent of decay and defects in trees. The instrument is essentially a battery-powered drill with an extremely fine bit (1.1mm diameter with a flat 3mm tip). The bit is driven into the tree up to a depth of up to 400mm. The energy required to drive the bit into the tree is measured and a graph is produced displaying the distance traveling into the wood on the x-axis and the amplitude (the torque) on the Y-axis. By examining the changes in torque required to propel the bit into the wood, it is possible to detect wood weakened by decay, cavities, cracks, and other defects.