Can't find the thread where people were asking about this, but I've re-found the tech doc link.

It has the levels at which the conception indicator change on p17 as:
Not Pregnant (0 mIU/ml), Pregnant 1-2 weeks (25 mIU/ml), Pregnant 2-3 weeks (200 mIU/ml) and
Pregnant 3+ weeks (20000 mIU/ml)

Although other sources state that the 20,000 is a typo, and should read 2000.

Hope this helps!

Cat xxx