I agree with your sentiments, _but_ all I know is that if you look at, e.g. the 1982 'microcomputers and memories' handbook, pg. 251, you'l see a three-backplane system, with terminations at the start _and_ end of the first backplane (and also at the end of the third backplane). I've seen other similar diagrams elsewhere, that's merely the first one I ran across in a quick search for this post. Like I said, I cheerfully admit that I don't really fully understand what's going on there in the analog domain, but I've seen this in more than one place in the DEC QBUS multi-backplane configuration instructions. Noel