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The Last Decimal / Myths
Six beliefs, checked

Six beliefs about rounding, checked

Six beliefs a reader is likely to arrive with, each checked against the samples on this site. Four fail, one is half right, and one is right for a reason worth stating.

Open the partner accountWhat rounding cannot do
Sample spec
beliefs
6
false
4
partly
1
true
1
the unitThe smallest amount the currency can express. In a two-decimal currency it is 0.01; the increment a stake must take is coarser and published per market.
the directionWhich way each rounding goes: down on a stake and a return, up on a duty and down on a prize. It is a rule, published, and it decides who keeps the fraction.
the volumeOne unit per event is nothing once and a figure at scale: on the samples, two thousand events of the same size retain 60.00 from the digits alone.
Direct answer

Four of six common beliefs about rounding are false: that it is a fee, that round numbers avoid it, that the shown balance is the balance, and that the two directions cancel out. One is partly true - it is too small to matter on a single event - and one is true: the direction is set by the operator's rules and not by chance.

The six beliefs

1. Rounding is a fee

False. A fee is charged and appears on a line; a rounding leaves the fraction unplaced and shows it nowhere. On sample B the 0.24 tail never left the account, and on sample H the 60.00 accumulated from money that was never staked.

false

2. Round amounts avoid it

False in general, true only against the increment. A request of 5.00 lands whole, but the same player typing 10.33 on a 2.50-increment market leaves 0.33, and the same digits leave nothing on a 0.10 market. It is the market's increment that decides, not the roundness of the number.

false

3. The shown balance is the balance

False. On sample D four of eight accounts displayed more than they held and three displayed less, and on sample I an account holding 0.00499999 displayed 0.00. The shown figure is a rendering of the value, not the value.

false

4. The directions cancel out

False. On sample G the duty was rounded up and the prize rounded down, so the two reinforced; on sample H both the stake and the return were rounded down. Cancellation would require the two directions to meet on the same event, which the rules do not do.

false

5. It is too small to matter

Partly true. On a single event of one unit it is not worth arguing about, and it is far smaller than the margin any betting product carries. At volume it is a figure: 60.00 from two thousand events on sample H, and 1.2% of the stake turnover that produced it.

partly

6. The direction is a rule

True, and worth stating. Whether a stake rounds down or up, whether a duty goes up and a prize down, is a decision published in the operator's rules. It is not chance and not a mistake, so it can be read before it is experienced.

true
the six beliefs against the arithmetic false (belief 1): tail 0.24 never left the account → not a fee false (belief 2): 10.33 leaves 0.33 on a 2.50 increment → roundness is not enough false (belief 3): 4 of 8 balances disagree with their shown figure false (belief 4): duty up + prize down reinforced to 0.0335 partly (belief 5): 0.01 per event, 60.00 per two thousand true (belief 6): the direction is read from the rules document

The pattern behind the four false ones

All four false beliefs share one mistake: they treat the rounding as a mystery to be felt rather than a rule to be read. Once the increment, the direction, the display precision and the credit unit are found in the rules, none of the four survives, and nothing has to be taken on trust. The fifth belief is the one that needs care, because it is true and false depending only on the number of events - which is the subject of its own page in this desk.

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What rounding cannot doThe limits, stated positivelyThe volumeWhy belief 5 needs a number of events to answerQuestionsTwelve questions answered in full