and frame are often used synonymously which may lead to some confusion. To the user of course a node is the same as a page and they are both identified by a 'page' number. To access a particular item of information, a simple progression down through the nodes to the page is all that is required, and then the frames of that page can be stepped through. This is facilitated by each node displaying up to ten choices, one of which may be taken by the user responding with the appropriate digit from 0 to 9. This simple method of access may be thought of as a question and answer session: the computer displays a question 'Which of the ten choices do you want to make?’ and the user replies with the appropriate digit. A choice of 9 at node 17 moves the user to page 179. The flexibility of this logical access method is increased firstly by allowing cross-referencing from one branch of the tree to another and secondly by providing a few simple commands available to the user for accessing certain pages directly. While this principle had considerable advantages in user simplicity and computer efficiency over the "keyword/thesaurus principle" used in many other systems, it has two very real disadvantages which have now been recognized: lack of flexibility; slowness. Page numbers were from one to nine digits in length, i.e., in the range 0 to 999999999 created in a tree like structure, whereby lower level pages could only exist if the higher numbered "parent" pages had already been created. Thus creating page 7471 required pages 747, 74 and 7 to exist, but generally the three digit node 747 would have been created in order to register the relevant main IP account. Single and double digit pages were special pages reserved by Prestel for general system information purposes, as were the 1nn-199nn sets of three digit nodes e.g. page 1a was the standard Prestel Main Index. Pages starting with a 9 were for system management functions, and were limited to three digits in length. e.g., page 92 showed details of the users Prestel bill, and page 910 gave IPs access to online editing facilities. Available characters consisted of upper and lower case alphanumeric characters as well as punctuation and simple arithmetic symbols, using a variant of ISO 646 and CCITT standard. This layout was later formalised in the 1981