Ah, yes - lines through the zeros and all that. We actually had a mainframe at my comprehensive - it had been donated by one of the town banks to the grammar school, which was then combined with the secondary modern, so one of the classrooms in the building used for the first two years was full of something that wouldn't hold up to a palmtop these days - I've no idea what it was used for, when we had a programming class the scripts (filled in on grid-ruled paper) had to be sent to the main council education department computer for processing (or not, since the teacher forgot a vital step).