Curved / Gyroscopic

For curved microtunnelling, gyroscopic systems may be used - involving a north-seeking gyro-compass to track horizontal alignment and a remote water level gauge system for vertical alignment. As the diameter of the tunnel increases other options involving automated target-seeking theodolites can be used for positioning in curved alignments and hand surveying can also be used. Where possible, hand surveying is often used periodically for calibration or quality control checks of automated systems.