I have just looked and Coinmill is 2 decimal places.
Yahoo Finance is to 3 so we could use that.
If thats the way to go I would sugest all guesses so far are taken to 3 decimal places by adding a zero to the end.
It's not my competition though so would need Scunner to change ruling if seen fit as he started it.

Agree H that we should not restrict bidders as they are few and far between, ie less than 2% of the readers of the topic.
