The great majority of books received on electronic legal deposit (eLD) come in EPUB format. While this has advantages in terms of long-term preservation of the text, it does mean that such ebooks lack page numbers, rendering traditional methods of citation impossible. This issue has been raised as a matter of urgent concern by the legal deposit libraries, including Cambridge. Meanwhile it is suggested that reference is made to chapter and paragraph number.
Journal articles received on eLD are mostly in PDF format and so have page numbers, as do those eresources (books and journals) to which Cambridge University Library subscribes.
For information on how to cite, please see http://libguides.cam.ac.uk/cambridgeebooks/cite.
For other options see under Alternatives.