JFC, I don't know about any link but I have the paper in front of me (Mon Courier 04/02/08).I shall type in what it reads. (Bear with my limited computer skills)

Quote
"In recent weeks we have had an unusually high number of punters asking us how to explain the percentage deduction system for UNITAB.
We did try to get a definitive answer but the best we can do is there are no longer set deductions from any TAB pool.
UNITAB is not the only one which operates on a system where it must return a minimum 75% (a 25% deduction) on any given bet but over a year must return 84 % (16% deduction) of all money invested.
The safeguard is the TAB must remain competitive with the other TAB's in declaring their dividends.
They also point out they have to pay tax and expenses out of the 16% they take each year.
But how each bet's calculated- who knows!
Unquote

You could ring UNITAB, but I think Mark Oberhardt would have got to the bottom of this, if there as one.

PS That took me an age to type.