Bronze, silver, gold and platinum

A brain's colour tells you how long your streak is. There are five of them: a plain pink brain for a streak that has not yet reached a week, then four metals for the milestones that follow.

The four milestones

• Bronze: a week. Seven days in a row. This is the first real milestone, and you meet it quickly: a full week without a miss.
• Silver: a month. Thirty days in a row. About four and a half weeks, and the point where a daily habit starts to feel settled.
• Gold: a season. Ninety days in a row, roughly one season of the year. A real commitment.
• Platinum: a year. Three hundred and sixty-five days, without missing one. It is a cool white-blue, deliberately the quietest of the five: the shine of something that has simply been there all year.

The colour follows the length, and only the length

The metal is worked out from how many days long your current streak is. It does not depend on how hard the days were; that is the job of the brain's size. So you can read your brain in two parts: the size says how hard the days in your streak got, and the metal says how long you have kept going.

The two meet in an easy way. A streak of a week or more already contains every weekday, so it always has the largest size. After the first week, the size stays put, and the colour is what shows your progress.

A new metal is a moment

When a solve takes your streak past a milestone, the game marks it with a short celebration on the result screen, announcing the new brain by name. Each milestone is celebrated once.

When the streak breaks

Your brain goes back to plain pink and starts again. But the game remembers your best streak, with its length, its dates and its metal, in the same help screen. A gold streak that ran from October to January is still gold in your record, even after it has ended.

Is it fair?

These milestones were chosen to be reachable and honest rather than easy. The metals were once tied to the weekdays you reached in a streak's second week, which made gold possible after eight days. That was too quick to mean much, so they now follow length: a week, a month, a season and a year. The brain is always worked out from your history of solved days, so the change simply re-read your record, and nothing was lost.