Ever backed a selection online, and noticed a rule four reduction on your betslip?
Or have you ever had a winner at the racecourse but not picked up as much money as you expected?
Look no further, we are here to explain why 'Rule 4' is in place.
Rule 4's form part of the Tattersalls Committee terms and conditions of betting on horse racing, which compensates a bookmaker if a horse is withdrawn prior to a race.
If a bet is placed beforehand on say, a 6/1 shot in a three-runner race, but a 5/4 shot is subsequently withdrawn, the 6/1 odds are no longer a fair reflection of that horse's chances of going onto win.
Rule 4 deducts a set value in pence out of every pound in winning bets, with the size of the deduction determined by the price of the non-runner.
The level of deductions ranges from 90p in the pound at 1/9 or shorter, to 5p in the pound at odds of 10/1 to 14/1.
Any horse above the odds of 14/1 is deemed not likely enough to play a part in the outcome of the result.
As a result of the confusion, a new initiative was trialled at Doncaster on Saturday by Christopher Hudson - who issued small printed cards to customers, explaining the impact Rule 4 would have on their selection.
(Credit: Racing Post) Hudson said: "With the acrimony that there has been about gambling at the moment we want to do everything we can to help people.
"It has been agreed with the RCA. The Gambling Commission were keen too, they like openness and it is another way of educating people.
"It saves time and a lot of bother if there is a dispute, perhaps on a busy Saturday in the summer when they have had a bit of booze and a customer asks why there is 10p in the pound off.
"The idea is that the days of the professional punter on the racecourse are going and we want to help the recreational racegoer," he said.