How to read the PC success rate
What the success rate shown in Perfect Clear Mode really means, and how to read 0%, 100% and the numbers in between when choosing your move.
In Perfect Clear Mode, a PC success rate is shown beside the board: a number such as 70%, 35% or 100%. This number does not say how good you are. It describes the luck of the pieces you cannot see yet. Once you know what it means, you can tell which move to choose, and whether a failure was your own fault or just bad luck.
What the success rate represents
Whether a perfect clear is possible depends on the shape of the board and the order of the pieces still to come. Of that order, you can see the current piece, the five next pieces and the hold piece. Beyond that, you cannot see. But because of 7-bag, the hidden pieces can only come in a limited number of ways, and each of those ways is equally likely.
The success rate is calculated like this.
- List every way the hidden pieces can come, following the 7-bag rule.
- For each one, check whether the best possible placements lead to a perfect clear.
- Show the share of those ways that can be turned into a perfect clear as the success rate.
Step 2 is the important one. The success rate is the number you get if you keep making the best move. The calculation even takes into account that, each time a new piece comes into view, you choose your placement again using what you know at that point.
An example you can check by hand
The success rate here is 50%. The next piece is equally likely to be the O or the I. If the O comes, hold the T and place the O that appears, and you have a perfect clear. If the I comes, nothing you do will fill the 2×2. One of the two cases succeeds, so the rate is 50%.
On the same board, things change if the O is visible. If the current piece is the O, it is 100% (just place it). If the first piece in the queue is the O, it is also 100% (hold the current piece and place the O). And if you can see that no O will come by the next piece, it is 0%.
How to read the number
| Shown | Meaning | What to do |
|---|---|---|
| 100% | Whatever the hidden pieces turn out to be, there is a way to reach a perfect clear. | Follow the recommended placement and you always succeed. Ideal for practising building the plan yourself. |
| 50–99% | Some orders of the hidden pieces lead to failure. | Even the best moves can fail. A failure does not necessarily mean you played badly. |
| 1–49% | It only succeeds when particular pieces happen to come at the right time. | In a real game, a sign to give up on the perfect clear and switch to another plan. |
| 0% | Whichever pieces come, in whichever order, there is no perfect clear. | Check what went wrong and retry the same drill. |
When does the number move?
It moves because of your move
If you place a piece somewhere other than the best spot, the success rate drops. If a 70% board becomes 40% right after you place a piece, that one move cost you 30 percentage points of your chances. Compare your move with the recommended placement and you will see which placement made the leftover shape worse.
It moves because a new piece appears
Each time you place a piece, one new piece appears at the end of the queue. If it is a helpful piece the success rate goes up, and if it is an unhelpful one the rate goes down. If the number drops right after you made the best move, that is not a mistake. The luck simply fell the wrong way.
As long as you keep choosing the best move, the rises and falls cancel out on average. The trick is to tell the two apart: did the number drop because of the move you made, or because of the piece that appeared?
Whether to hold is also decided by comparing success rates
The “Why hold” box shows two success rates side by side: one for placing the current piece as it is, and one for holding. In the 2×2 example above, if the current piece is T and the first piece in the queue is O, placing directly gives 0% and holding gives 100%. When the difference is this large, the hold is essential. When the difference is small, you know that either choice is fine.
The opening perfect clear only shows “possible” or “impossible”
An opening perfect clear starts from an empty board, and the number of ways to place the pieces runs into the millions, so an exact success rate cannot be calculated in an instant. The opening drill therefore shows a verdict instead of a success rate: PC possible / PC impossible. The verdict answers one question: with the piece order you can see, is there at least one way of placing the pieces that leads to a perfect clear?
As you place pieces and the number of hidden pieces falls to two or fewer, the display switches to the same exact success rate as in the leftover drills.
What the number does not tell you
- It does not include how hard the inputs are. A plan that needs a spin-in is counted as if the piece can simply be placed.
- It ignores time limits and gravity. The number assumes you have plenty of time to think.
- It only covers perfect clears that are completed within four rows.