shares are purchased in the market at the time the dividend is paid or shortly after, in this case the 29th October, at the prevailing price on the day. No calculation involved.
Unusual to see a price rise on the day a share goes ex-dividend though.
Been in here since i got my free ones. In here long, long term. Not to bothered by a few dips along the way. In the long term i cannot see SL staying this low.