Streaks and the calendar 日々
What the streak counts, and the year of squares that shows what a single number cannot.
A streak counts the days you studied in a row. It resets when you miss one. That is the whole rule, and it is worth stating plainly because streaks are the mechanic most often bent into something else.
Where the day ends 時差 time difference
A streak is counted in days, so it matters which midnight ends one. Yours is whichever midnight belongs to the zone on your account page. Until you set it, that is UTC - which is nine in the morning in Japan and one in the morning in Belgium, so it is worth setting if you live far from Greenwich and study late.
The same boundary decides when the daily unlock comes back and when the shop rotates, so it can be changed once every thirty days rather than freely. A boundary you could move at will would be a way to take a second unlock, or to give a streak about to break another night - and a streak that can be rescued by changing a setting is not a record of anything. The first time you set it is free.
What a streak cannot do here
It cannot be repaired with money. There is no streak freeze to buy, no gem that undoes yesterday, and no notification implying you have lost something you can purchase back. A streak that can be bought is not a record of anything.
It also unlocks no learning material and gives no advantage in reviews. It is a record, and records are allowed to be simply true.
The one number is not enough
A streak says how long the current run is and nothing at all about the shape of the habit. Twelve days could be your best fortnight in a year or a shadow of the two hundred days before it. And the day it breaks, it tells you the worst possible thing: back to zero, as though the rest had not happened.
So the dashboard also carries 日々 days - a calendar year, one square a day, shaded by how much you did. It answers the questions the counter cannot. Whether a broken streak was one missed Tuesday or a month away. Whether your good weeks are weeknights or weekends. Whether this month looks like last month.
Every square is a day you turned up, and they stay there whatever the counter says. It is free, for everyone: a learner who has just lost a streak needs the evidence that the rest of it happened rather more than a subscriber does.
The shading
The five shades are fixed thresholds (nothing, under ten reviews, under twenty-five, under fifty, and fifty or more) rather than a scale relative to your own best day. A relative scale makes a quiet fortnight look industrious and a heavy one look flat, which is the opposite of what the picture is for.
It runs January to December rather than as a rolling year, because a year with a name is something a person can finish, and the months still to come read as room rather than as failure.
Going away on purpose
If you know you will be away, a rest 湯治 holds your streak and moves your schedule with you, so a holiday is not a choice between your habit and your fortnight off.