Some Sudoku apps offer three levels. Some offer five. Some offer seven, with different names for each one (gentle, easy, medium, medium-hard, hard, expert, master, and so on). Sudoku BLA offers four. Easy, medium, hard and expert. That is a product decision, and there is a reason behind it.
The reason starts with an editorial standard at BLA: every product decision starts with the question "would the person using this pick this app as their main app for that function?". For Sudoku BLA, that unfolds into something specific: someone who plays Sudoku wants to level up with criteria, not with artificial label inflation. Seven differently named levels is inflation. Four levels with a real jump between each is criteria.
Level 1, easy. For someone learning, or for someone who wants to finish a Sudoku in five minutes while the coffee brews. Most of the clues are already on the board. Two techniques are enough: naked single and hidden single. You almost never need to take notes. It is the level where the game teaches you to read the board.
Level 2, medium. Starting clues drop, and the first new technique kicks in: naked pair. You need to mark candidates to see the pairs appear. Average round time: fifteen minutes. It is the most played level in any Sudoku app in the world, and Sudoku BLA has two thousand puzzles here. It is the sweet spot between time spent and the satisfaction of closing.
Level 3, hard. Advanced techniques start: pointing pair, X-wing. Starting clues are few. You need to mark everything, eliminate everything, and follow the deduction chain for longer. Average round time: half an hour. It is the level where Sudoku stops being a puzzle and becomes a chess match against yourself. When you finish a hard one with no hint, you feel that kind of quiet pride only logical games deliver.
Level 4, expert. Five to eight starting clues. Advanced techniques in sequence. Average round time: an hour or more. It is not for everyone, and the app does not pretend otherwise. It is for someone who has played Sudoku for years and wants a puzzle that lasts a full sitting. In Sudoku BLA, expert is where the board turns into extended meditation. You open the app, pick an expert, and dedicate however much time it takes.
Why stop at four? Because a fifth level would be redundant. Any puzzle harder than expert demands techniques so specific (X-chain, swordfish, coloring) that it stops being Sudoku and turns into another game. The user who wants to go further finds plenty in the two thousand expert puzzles of Sudoku BLA. The average player takes more than five years to finish them all. And when they finish, they start over. The puzzles were generated with unique solutions; solving again is satisfying because you forget the path.
Four levels, two thousand puzzles each, eight thousand total. Works offline. Available on the App Store on iPhone, iPad and Mac. Easy for those starting out. Expert for those who have played for twenty years. That is the whole point: four categories, each with depth. Instead of seven categories with shallow depth.
