I hear a lot from colleagues from other disciplines that blackboards are antiquated and why not use computer projections, e.g. pdfs
(in maths of course we would not use powerpoint, but write them with latex as we do for conference talks). When reading computer slides in a lecture or talk, I get terribly confused if there is too much written on them. For me, computer slides should have bullet points or a few very short clear sentences. (Shortish) definitions can go on computer slides, I’ve done that for talks. But if I were to write out a proof on a slide like that, it would take at least three or four slides, and then the lecture audience would not be able to see the beginning of the proof, let alone the statement of the result, once I’m past the first slide. In general (in this instance, meaning in CMS lecture rooms), I find blackboard the perfect medium for displaying a lot of information at once, i.e. writing out and developing the notes/proof as I go along, but being able to refer back to a definition earlier when I need it in a proof later, or the statement of the proof, or a previous result…. (if the blackboards are big enough that these things are still there, which in CMS they usually are). In Cockroft, the situation is a little different: the blackboards don’t move, are quite low, and the room is huge, so you’d have to write very large so that people at the back can see, and you couldn’t use the left side because people on the right wouldn’t see it, and you couldn’t use the right side, and you can’t write at the very bottom because it will be hidden for some people,… So by the time you’ve taken all that into account, there is not much more space there than on the overheads combined. And the overheads are at least projected high up and visible from (almost) anywhere in the room.