Is a spinning wheel really random?
How an online wheel picks a name, why the spin cannot be rigged by timing, and what makes a draw fair. Spin a fair wheel in your browser, nothing sent.
By Suraj Kumar4 min read
A wheel looks like chance at work: it spins, slows and ticks to a stop. On a screen, though, the wheel is a picture, and what matters is how the pick behind it is made. Here is how a fair one works, and how to tell.
The pick is made before the wheel moves.
On KeepSimp's wheel, pressing Spin first draws the winner from your browser's cryptographic generator, the same one that makes encryption keys. Only then does the wheel turn, a few whole times and then to a point inside the winner's slice, drawn from the same source and kept away from the slice's edges, so it never looks like a near miss.
That means how hard or how long you press changes nothing, and neither does the wheel's starting place. The animation shows the result; it does not decide it.
Every entry as likely, by rejection.
A computer's random source gives whole numbers in a fixed range, such as 0 to 4,294,967,295. Dividing by the number of entries and keeping the remainder favours the first entries slightly whenever the range is not a whole multiple of the count. The fix is to throw away the few numbers past the last whole multiple and draw again, which is what this wheel does, so each entry has exactly the same chance.
Give an entry more chances (“Pizza: 3”) and its slice grows to match, so the wheel always shows the real chance.
How to tell a wheel is fair.
From the outside you cannot see how a site draws, so ask what it says and whether it can be checked. Prove it, under More options, shows a fingerprint of the next draw before it is made and a record afterwards that anyone can use to make the same draw again.
Further reading
Topics: spin the wheel · is wheel of names random · wheel spinner rigged · random picker · fair random wheel · picker wheel
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