Any compass that determines direction by local magnetic anomaly; used where relevant charts are available and where a planet's total magnetic field is unstable or subject to masking by severe magnetic storms.

A paracompass is "any compass that determines direction by local magnetic anomaly; used where relevant charts are available and where a planet's total magnetic field is unstable or subject to masking by severe magnetic storms."

Paul and Jessica used one on Arrakis to find their way through the desert.