Peter,
I did read some stuff about the Anstey limit calculations but it was a while ago and I don't remember the details.
I've been happy using the method described by Ray (Shiraz) here:
http://www.iceinspace.com.au/forum/s...d.php?t=117010
I was able to derive the same result from the basic noise equation and convince myself that it works.
Cheers,
Rick.