OK, so no one knows the answer to my first question, so here's another.
There are 10 candidates but no one has 50% of the first preference votes. One candidate is eliminated and his votes are redistributed based on the second preference of his supporters (lucky them, two bites of the cherry!)
Still no one has 50% so the second last candidate's votes need to be redistributed.
On the second last pile of votes you now have all the ballot papers which put the second last candidate as first preference plus all the ballots which put the last candidate first, and the second last candidate second. So the second preference of the first set of votes needs to be considered, and the third preference of the second set of votes.
Question: what do you do with ballot papers which put the second last candidate first, but the already eliminated candidate second?