e-Nautical Publications (e-NPs) are digital versions of paper Nautical Publications. They are e-Books but differ in the fact that they are updated and sold as a data service on a twelve month subscription rather than per edition. ADMIRALTY e-NPs are encrypted PDF versions of their paper equivalent; they look identical. This is essential in order to demonstrate that Notices to Mariners (NM) corrections have been made and the publication is compliant.