My six spring clutch started slipping, so I stripped it down, applied the file where I had to, and reassembled it. I measured each spring, and there was some variation. Perhaps I should have bought new springs, but I wanted to ride the bike. So as at least a temporary cure, I arranged the springs as symmetrically as possible; the shortest spring went between the two longest ones, and so on.
Then I screwed the nuts on to each stud until the springs were all lightly and equally compressed, then tightened them all by the same amount. I cannot remember what this amount was, but it was governed by the nut on the longest spring. So if that spring was 40 thou shorter than it should be, the nut had to be threaded 40 thou further on to the stud, compared with a new spring. If that meant (say) two and a quarter turns of tightening for the longest spring, then all the nuts were tightened two and a quarter turns.
The result was a clutch that hasn't slipped now after hundreds of miles, which needed no further adjustment to lift squarely.
