1 Guinea = 1 Pound 1 Shilling Castle Rushen

Castle Rushen was one of several small Manx private issuers operating before the Isle of Man Banking Company consolidated much of the island's paper currency in the nineteenth century. The guinea denomination — one pound one shilling — is a peculiarly British institution, used in professional and trade transactions long after guinea coins had ceased to be struck, and its appearance on a provincial private note from a jurisdiction outside the Bank of England's reach reflects how deeply embedded the unit was in commercial practice.

The 1790s dating places this squarely in a period when counterfeit detection on small private issues was nearly impossible for ordinary recipients.