In essence it is the same restriction that we place on readers copying our books as set out in the copyright declaration at the beginning of all our books.
The CD contains the same data as the book and its main value is the ability for searching quickly, particularly by type, c/n and identity. We know that one of the first ERH CDs was copied and distributed among other enthusiasts who had not purchased the CD, which at that time was available separately. Since then we have made the CD copy-proof, and obtainable only by buying the book.
Earlier this year the Editor of ERH had a conversation with a Member who had tried to copy parts of the CD and complained about the quality! When he was made aware of the copyright conditions, he apologised and promised to delete any parts that he had copied into his database.