Over the last couple of years I have been bashing my local reserve (sadly neglected this year!) and recorded just over 1000 species there. Inevitably in that time I have discovered county firsts and one first for Scotland. This leads me to the conclusion, albeit hasty, that there is a ratio of new things you will find for any given number of species. Each site has produced one species new to Scotland. Each has produced several new to county. I'd bet these ratios are more or less similar. I am dubbing these "The Shuttleworth Ratios"until I find out somebody else has called them something else. Obviously these will vary depending on where you are.
The exciting thing about this is that I have a chance to prove it in another square. 1000 species next year in a different square ought to produce something new for Scotland. Let's see. How many for new to Britain, or new to science - 5k? 10k?
Anyway, here you an see how good a record this is - well pleased with that!