Every webmaster knows that Google results vary from time to time. During the month there will be minor changes in rankings. This is called 'Everflux'. But only about once per month does Google dance, updating the back links and the PageRank. The dance usually lasts about 3-5 days. During these days results on Google tend to change by the minute. After the Google Dance is over each site will have been adjusted in rank.

Google is *VERY* interesting. It is highly inconsistent and extremely erratic - yet few notice and no one cares. See for instance http://google.fergusons.dk/

Google is not just one homogeneous database with the kind of consistency you require to run an enterprise. It's LOADS of databases, which are all updated on the fly and out of sync with each other. The expression used on the web site cited above - "the Google dance" - is a brilliant description. It can be very confusing - you do a Google search and spot an item. An hour later, you realise it was more useful than you thought and try to find it again. And you can't.

The major Google databases have a cycle supposed to be four weeks but actually closer to nine. Exactly which database you get when you type in your search is in the lap of the gods.