FremgangsmÕte og apparat for Õ etablere en magnetisk pol for retningsbestemmelse

摘要

A magnetic observatory device (10) is deployed at a fixed location such as the sea bed (22) to provide data measuring variations in the local earth magnetic field. This data is used to correct information from magnetic direction sensors, for example in a measurement-while-drilling system (28) of a drill string (26). Also described is a reference apparatus for initial calibration of the device (10).