How your list ranks itself

You never drag levels around. Each time you add a level, you answer a few questions like “Which one is harder?”. Your answers decide where the level goes. Later, re-checks keep the list correct as your skill changes.

Placing a level

The new level is compared with the level in the middle of the part of your list where it can still go. If the new level is harder, it goes somewhere above that level. If it is easier, it goes somewhere below. Each answer removes half of the remaining positions, so the questions stop quickly:

• A list of 10 levels takes about 4 questions.
• A list of 100 levels takes about 7 questions.
• A list of 1000 levels takes about 10 questions.

About the same stops the questions at once, and puts the new level directly next to that level. Your first level needs no questions. If you select the wrong answer, use Undo last answer.

Rating

Each level has a rating, and the list is sorted by it. A higher rating means a harder level. The system is similar to the Elo ratings that are used in chess. A new level gets a rating between the levels directly above and below it.

A re-check changes the ratings of both levels in it. When you say that one level is harder than another, the list always puts it above that level. If you compared the same two levels more than once, your latest answer counts.

Uncertainty

The ± number next to a rating shows how sure the list is about that rating. Each comparison makes it smaller. It grows a little each day that you do not compare the level. A level with a large ± moves further at its next comparison, so levels that you have not checked for a long time can find their new position quickly.

Re-checks

As you get better, levels that felt hard can feel easier. Re-checks find these changes. A re-check is due when:

• A level is stale: you did not compare it in the last 60 days.
• Two levels contradict your answer: other comparisons moved them, and now the list has them in the opposite order from your last answer about them.

A re-check asks about levels that are near each other on your list. You can re-check at any time, also when nothing is due. If a level is in a very wrong position, select Re-place on its page to place it again from the start.

History

Every change to your list is recorded. The History page shows what changed and when. The page of each level shows its position over time and every comparison you made with it, so you can always see why a level is where it is.

Add a level to try it.