Abstract: Provided is a device for monitoring the orientation of a hand-held surgical or dental tool. The device includes one or more orientation sensors that generate signals indicative of an orientation of the device. A processor calculates from the signals a current orientation of the device, where the current orientation is specified by a unit vector defined by a first angle formed between the unit vector and a predetermined first fixed axis and a second angle formed by the unit vector and a second predetermined axis. The processor compares a current orientation of the device with a predetermined reference orientation of the device stored in the memory and provides an indication of the deviation between a current orientation of the device and the reference orientation.