The Magnetic Field Variation Database is loaded as part of the navigation database, but is copied to, and resides within each ADAHRS. When applying power, the system compares the MV DB within the navigation database to that presently residing in each ADAHRS. When a new navigation database is loaded, the system may ascertain the newly loaded MV DB within the navigation database is newer than that residing in each ADAHRS. In this case, the system will prompt for an update with the system message 'Magnetic Database Out of Date: Update Navigation Database to resolve this issue' on the 'Messages' Window.