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The Last Decimal / The unit
The smallest permitted stake

The unit and the increment

Before any bet is priced, an operator decides the smallest amount of money that exists in an account and the steps a stake may take. Those two numbers are published in the rules and rarely read, and they decide more of the arithmetic than the odds do.

Sample spec
markets
8
increments
7 distinct
min unit
0.01
largest tail
0.33
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

The smallest unit is the smallest amount of money the currency can express - one cent, or one hundred-millionth of a coin. The increment is the step a stake must take, published per market, and the minimum is the smallest stake the market accepts. A request is rounded down to the increment and refused if it is below the minimum, so the same request places a different stake on each market.

Three numbers, not one

It is tempting to treat "the smallest stake" as a single figure. It is three. The unit is what the currency can express: an account in a two-decimal currency cannot hold a fraction of a cent as money, and an account in an eight-decimal currency can. The increment is the step a stake is allowed to take on a given market, which is a commercial choice and is usually coarser than the unit: 0.10, 0.20, 0.25, 0.50, 1.00, 2.50 or 5.00. The minimum is the smallest stake the market will accept, which is a separate published number and is sometimes higher than the increment. A market can therefore accept 2.00, 3.00 and 4.00 but refuse 1.00 even though 1.00 is a multiple of its increment.

Sample A - the three numbers on eight invented markets
MarketUnitIncrementMinimumWhat 10.33 becomes
m10.010.100.1010.30
m20.010.200.2010.20
m30.010.250.2510.25
m40.010.500.5010.00
m50.011.001.0010.00
m60.012.502.5010.00
m70.015.005.0010.00
m80.011.002.0010.00

Seven distinct increments appear across eight markets, and one of the eight raises its minimum above its own increment. The unit is the same everywhere, which is what makes the increment the number that actually bites.

sample A - why the minimum is not the increment m8: increment 1.00, minimum 2.00 a request of 1.00 is a whole multiple of the increment → but 1.00 < 2.00 → refused a request of 2.00 is a whole multiple → and 2.00 ≥ 2.00 → placed as 2.00 so the increment says which amounts are shaped correctly and the minimum says which of them are big enough; a stake must satisfy both.

What this means for a reader

The practical consequence is that "the amount I typed" and "the amount I placed" are two different numbers, and the gap between them is money you did not stake and cannot see. On sample A the same request leaves a tail between 0.03 and 0.33 depending only on the market. Nothing in the interface announces this: the tail is not a fee, it is not a line on a statement, and it does not appear anywhere as money. It is simply the part of the request that was never placed.

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