How to Play Stacked Formula

Stacked Formula is a mental-arithmetic time attack: you solve expressions one after another as fast as you can. It is less about whether you can do the maths and more about how long you can keep going without your hands stopping.

Every answer is a single digit

The defining rule of this game is that every expression resolves to a number between 0 and 9. That means one tap on the keypad submits your answer. There is no typing "12" and then pressing a confirm button, so typing speed never decides your time. What the clock measures is purely how long it takes you to arrive at the answer.

On a computer you can also answer with the number keys on your keyboard.

You can see what is coming

The screen holds five rows of problems at a time, and the bottom one is the expression you are answering now. Each answer moves the stack down by one row. The next problem, and the one after that, are already visible. The game is built so that players who can glance at the next line while finishing the current one get faster. This is where your time is won.

Levels and problem counts

There are six levels, all unlocked from the start. They differ in how many numbers appear and which operators are used.

You can choose 20, 30 or 50 problems per run. Best times are recorded for each combination of level and problem count, so "3+- with 20 problems" and "3+- with 50 problems" are tracked separately.

Rules of the expressions

• The numbers used run from 1 to 9. Zero never appears as a term.
• Standard precedence applies: × and ÷ first, then left to right among equals. There are no parentheses.
• Division always comes out even. You will never see a fraction or a remainder.
• Intermediate results may be two digits or negative. Only the final answer has to land between 0 and 9, so expressions such as "9+8−9" or "1−2+3" do appear.
• On levels that include × and ÷, every expression contains at least one × or ÷. Pure addition-and-subtraction expressions are never mixed in.

The penalty for a wrong answer

A wrong answer locks the keypad for one second, and the problem stays on the stack. Guessing costs you twice over: you wait, and the problem count does not go down. When only a few problems remain, taking a breath and pressing with certainty usually finishes the run faster.

Five ways to cut your time

1. Read the next line while solving the current one. This matters more than anything else. Starting a problem from scratch after each tap, versus having already read it, is worth close to half a second per problem — around 25 seconds over a 50-problem run.
2. On × ÷ levels, find the operator first. Since at least one × or ÷ is guaranteed, locating it and resolving that part first makes the whole expression fall into place.
3. Use the fact that the answer is one digit. If an expression opens with "8×7", you know a large division or subtraction has to follow. Sometimes you can narrow the answer down before finishing the arithmetic.
4. Warm up on a short level. A few runs of 2+- with 20 problems settle your fingers onto the keypad and cut mistaps.
5. Match the keypad to your habits. In settings you can switch between the calculator layout (789 on top) and the phone layout (123 on top). Choosing the one you already use every day visibly reduces mistakes.

Records and ranking

Best times are saved on your device and submitted to the online ranking. The ranking screen shows the top 20 and your own position for each level and problem count. The pyramid on the result screen also shows roughly where you sit among all players.

You can optionally link a Google account from the settings screen to tie your records to that account. The link is used only to carry records across devices — no mail is sent and no contact details are collected. If the account already holds records, you will be asked to confirm before this device's records are replaced by the account's.

A small thing to find

An ink-painted owl is perched above the start button. Tap it and it flies off — but the game quietly counts how many times in a row you managed it. Reach five and a new item appears in the settings screen.

Add to Home Screen

On iPhone and Android, choose "Add to Home Screen" from the browser's share menu to play full-screen like an app. Pages you have opened once are stored on the device, so solo play works even without a signal (features that need a connection, such as the ranking and Google account linking, become available when you are online).