A gravity dependent pedicle screw tap hole guide comprises a guide shaft maintainable parallel to a drill bit during the drilling of a pedicle screw tap hole; an accelerometer associated with a reference direction and responsive to gravity to determine an angular difference between an acting direction of gravity and the reference direction; and a mounting attaching the accelerometer to the shaft and establishing a positional relationship between the reference direction and the longitudinal axis. The accelerometer is preferably in communication with a data processing device or system, which data processing device is able to use signals from the accelerometer to perform one or more actions, such as, for example, displaying the angular difference.