The UniTAB will tell us that its 114%
But with the rounding down , this now makes it 118.5%

If looking at Betfair
If market is say 105%
We could add the 5% comm to that which makes it 110%

Here's a method I find that works well with this percentage difference.

Pull up the Betfair site.
Go to live prices where the TABS prices can be compared to Betfair prices.
Click onto SuperTAB header, this now sets the price ranking for them.

At 1 min mark
Compare Super TAB top 4 prices to Betfair price , which will be right near its column.
Bet 1.30 units on the overs (greater price on Betfair than SuperTAB)
Bet 1.00 units on the unders. (lesser price on Betfair than SuperTAB)

No odds on races.

This works well if the Favs don't win all day.

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Cheers.