Calculator: rules

How a game works, which kinds of sums there are, what separates the three modes, how much thinking time each task gets, and how experience, streak and level come about.

The goal

Mental arithmetic against the clock. A sum appears, you type the result and confirm; the next one follows immediately. How long a game lasts and what a mistake costs depends on the mode; how hard the sums are depends on the kind.

How a game works

1. Pick a kind of sum, that is, the range the tasks are drawn from, and one of the three modes.
2. After "ready, steady, go" the first task appears. Type the result on the number keys; you only need the minus sign where terms can go negative.
3. Confirm with Enter. If the result is right, the next task follows immediately; if it is wrong, the mode decides what happens.
4. The game ends when the time runs out or a mistake ends it. You can quit at any time; a game you quit is not scored.
5. Then comes the summary: every task, your answers, the time you took per task and a verdict on the whole game.

The seven kinds of sums

They determine what the tasks look like, from a single multiplication to a term with six numbers. In every term kind, multiplication binds before addition, brackets can appear, and a division always comes out even: awkward fractions are not mental arithmetic, they are harassment.

• Small times tables: one multiplication with numbers from 1 to 10.
• Large times tables: the same with numbers from 1 to 20.
• Times tables XXL: numbers from 1 to 100. This is where knowing by heart ends and calculating begins.
• Small terms: two to three numbers up to 99, plus and minus only, no brackets.
• Medium terms: three to four numbers up to 99, all four operators, brackets possible.
• Large terms: four to five numbers up to 150, and with a probability of about six percent one of them is a square of a number up to 10.
• Extreme terms: five to six numbers up to 200, squares up to a base of 20. Without keeping intermediate results in your head, nothing works here.

The three modes

They decide how a game ends and what a mistake costs. The tasks themselves are the same in all three.

• Survival: no overall clock, but every single task has its thinking time. A mistake or an expired thinking time ends the game at once. What counts is how far you got.
• One minute: sixty seconds, as many tasks as possible. Right scores a point, wrong takes one away.
• Tick tack: you start with one minute. Every correct answer credits time, every wrong one deducts it, and the task stays until it is right. With every correct answer the credit shrinks by four percent, with every wrong one the penalty grows by five: the clock will run out, the only question is when.

Thinking time and time credit

Both depend on the kind of sum, because an extreme term needs more time than a number from the small times tables. The first figure is the thinking time per task in "survival", the second the credit for the first correct answer in "tick tack".

• Small times tables 10 and 2 seconds, large times tables 20 and 4, times tables XXL 30 and 6.
• Small terms 30 and 7.5 seconds, medium terms 45 and 10, large terms 60 and 20, extreme terms 90 and 45.
• In "one minute" there is no thinking time per task: there, only the one clock runs across the whole game.

Scoring and experience

What counts is the number of tasks solved correctly, weighted by the kind of sum: an extreme term is worth more than one from the small times tables.

• Experience comes from correct sums only. A wrong answer costs no experience, it simply earns none.
• Per correct task: 0.1 experience points in the small times tables, 0.2 in the large ones, 0.3 in XXL and in small terms, 1 in medium, 2 in large and 4 in extreme terms.
• Forty small times tables tasks are therefore worth exactly as much as a single extreme sum. Those after experience find it at the top, those after practice at the bottom.
• Rounding happens per game and upwards, but zero stays zero: 0.8 experience points become 1, a game without a single correct answer earns 0.
• Checking happens on the server. From the same seed it produces the same sequence of tasks as your browser and recomputes your answers. A game with easier, invented tasks fails that check.

The verdict

Every game ends with a sentence about your performance. It is not the score in words but a comparison with what counts as a good rate in that kind of sum.

• The yardstick is tasks per minute, and it differs by kind: 22 in the small times tables, 12 in the large ones, 14 in small terms, 8 in medium, 4 in large, 3 in XXL and 2.5 in extreme terms.
• Only that makes the verdicts comparable across kinds. Ten extreme terms a minute would be from another planet, ten small times tables tasks are below average.
• Within a class the sentence is picked at random, so the same performance does not get the same text every time.

Streak, level and history

• You can play without an account. Your games are still saved, but they belong to nobody.
• The first level up costs 20 experience points, the second 40. After that the price grows ever more slowly and approaches 500: the step from level 10 to 11 costs 173, the one from 20 to 21 costs 286.
• The flame burns on every day you played. A day runs from midnight to midnight German time, and if you last played yesterday your streak survives and you can continue it today.
• The streak applies to Calculator only, every game keeps its own. Experience, by contrast, is a single number across all games.
• The history holds every saved game with its tasks, your answers and the time you took per task. It also shows which kind of term you get stuck on.

Tips

• Work terms from left to right and remember only the intermediate result. Keep the whole term in your head and you will lose it.
• In "one minute" guessing does not pay: a wrong answer costs exactly as much as a right one earns.
• In "survival" calm pays. There is no overall clock, only the thinking time per task, and that is generous; a single mistake, on the other hand, ends everything.
• In "tick tack" the start is what counts. The credit is largest at the beginning and shrinks with every correct answer, while the penalty grows.
• For experience, the hard kinds pay. Four points for an extreme term are forty times a tenth for one from the small times tables.
• Squares are quickest learned by heart. They turn up regularly in large and extreme terms, and every square you work out costs you seconds you need elsewhere.