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A 30-second tour of what this guide covers and why it matters. The basic calculator does more than +, โ, ร, รท โ and most users never discover the rest.
Most people use a calculator for half its features. They miss the memory keys, never use Ans, and don't know that pressing = twice does something useful. This guide is the missing manual โ short, visual, and interactive.
Each section has a small demo you can play with. By the end you'll be faster, make fewer mistakes, and know exactly what every button on the keypad does. There's also a 5-question quiz at the end to test it.
How to read this guide
You probably know +, โ, ร, รท. The rest of the calculator can save you real time.
The four operations & order (PEMDAS / BODMAS)
Multiplication and division happen before addition and subtraction. Parentheses jump the queue. This is why 2 + 3 ร 4 = 14, not 20.
The calculator follows standard math precedence. Whatever you type, it evaluates parentheses first, then ร and รท (left-to-right), then + and โ (left-to-right). This is identical to how Excel, Python, and your high-school teacher do it.
The classic gotcha is mixing operations. People expect a calculator to evaluate "left to right" because that's how they read English. It doesn't โ it follows math rules.
When in doubt, add parentheses. They make your intent obvious and never produce a different result than you expected.
- 2 + 3 ร 4 = 2 + 12 = 14
- (2 + 3) ร 4 = 5 ร 4 = 20
- 20 โ 6 รท 2 = 20 โ 3 = 17
- (20 โ 6) รท 2 = 14 รท 2 = 7
The most common error
Parentheses are the safest way to control grouping. Use them whenever you mix +/โ with ร/รท.
Percent: the three patterns
Percent is contextual โ what it does depends on the operator before it. Once you see the three patterns, every percent calculation gets easy.
In everyday speech, "10%" almost always means "10% OF something." But which something? The base depends on context โ and a good calculator infers the base from the surrounding operator.
Pattern 1 โ bare percent: "10%" alone is just 10/100 = 0.1. No base needed; you're asking for the fraction itself.
Pattern 2 โ percent OF a base: "10% of 200" = 20. You're saying "compute 10% applied to 200." On the keypad you'd type 200 ร 10%, and the calculator gives 20 because ร treats % as รท100.
Pattern 3 โ percent ADDED to (or SUBTRACTED from) a base: "200 + 10%" = 220. You're saying "increase 200 by 10% of itself." The calculator infers that the base for 10% is the 200 right before the +.
- 10% = 0.1 (just the fraction)
- 200 ร 10% = 20 (10% OF 200)
- 200 + 10% = 220 (200 increased BY 10%)
- 200 โ 10% = 180 (200 decreased BY 10%)
Real-world translation
Why ร works differently
Always ask: "p% of what base?" If the operator is + or โ, the base is the number on the left.
Square root (โ)
Square root finds the number that, when multiplied by itself, gives you n. Most basic calculators include it because it shows up in geometry, statistics, and physics shortcuts.
The square root of n is the value x where x ร x = n. So โ16 = 4 because 4 ร 4 = 16. Press the โ button on the keypad to insert a radical, then type the number (or a parenthesized expression) inside.
The calculator handles non-perfect squares too โ โ2 โ 1.41421356, โ7 โ 2.6457513. The display strip shows the radical with a proper overbar, the way you'd write it on paper.
You can put any expression inside: โ(9 + 16) = โ25 = 5. Useful for the Pythagorean theorem (aยฒ + bยฒ = cยฒ โ c = โ(aยฒ + bยฒ)).
- โ1 = 1 โ4 = 2 โ9 = 3 โ16 = 4
- โ25 = 5 โ36 = 6 โ49 = 7 โ64 = 8
- โ81 = 9 โ100 = 10 โ121 = 11 โ144 = 12
Negative numbers under the root
| Expression | Approx | Where it shows up |
|---|---|---|
| โ2 | 1.4142 | Diagonal of a 1ร1 square |
| โ3 | 1.7321 | Equilateral triangle height |
| โ5 | 2.2361 | Golden ratio: (1+โ5)/2 |
| โ10 | 3.1623 | Decade ratio in audio (โ 10 dB) |
Press โ, type the number (or parenthesized expression), close the paren. Done.
Memory keys: your sticky note
Memory is one stored value, separate from your current expression. Use it to keep a number aside while you do other math โ like running totals, intermediate results, or "the bill" while you split it.
The four memory keys are M+, Mโ, MR, and MC. Together they implement the simplest possible note-taking: a single value you can add to, subtract from, recall, or clear.
M+ adds the current result to memory. Mโ subtracts it. MR (Memory Recall) inserts the stored value into your expression at the cursor. MC empties memory back to zero.
Memory survives the AC button โ only MC clears it. So you can clear your expression and start a new calculation without losing the value you stored.
- Step 1: 120 + 18% = 141.60 (the bill with tip)
- Step 2: M+ (store 141.60 in memory)
- Step 3: AC (clear; memory keeps 141.60)
- Step 4: MR รท 4 = 35.40 (each of 4 people pays 35.40)
- Step 5: MR รท 3 = 47.20 (or, if 3 people: 47.20 each)
When memory beats history
Running totals
M+ stores. MR inserts. AC keeps memory; MC clears it. One sticky note, four buttons.
Ans: insert the last answer
After you press =, the answer is committed. Pressing Ans inserts it into your next expression โ handy for chaining without retyping.
Type 12 + 5, press =, get 17. Now you want to compute "what's 17 ร 2?" One way: type 17 ร 2 = (retyping). Better: type Ans ร 2 = (no retyping, no copy/paste).
Ans only pulls from explicit = presses, not from live results that happen as you type. So you have to commit a calculation with = before Ans has anything to give you.
Ans is most useful in the middle of an expression. After =, the answer is already on screen โ no need to insert it. But if you're typing a new calc and want the previous answer somewhere in the middle, Ans gets you there fast.
- 12 + 5 = โ 17
- Ans ร 2 = โ 34
- Ans โ 4 = โ 30
- Ans รท 6 = โ 5
Ans vs typing the digits
Press = to commit an answer. Then use Ans anywhere in your next expression to refer to it.
The repeat-"=" trick
After A op B = result, pressing = again applies "op B" to the new result. Great for repeated additions (counting by 5s), repeated multiplications, or chained discounts.
This is one of those features physical calculators have had forever, but most people don't notice. After computing 5 + 2 = 7, pressing = again gives 9 (adds another 2), then 11, 13, etc.
Useful for: counting in steps (5, 10, 15, 20โฆ), compounding (apply 1.05 repeatedly for 5% growth), or repeated discounts (price ร 0.9 = first 10% off, = again = a second 10% off compounded).
If you ever get a surprising chain of results when you press = again, this is why. AC resets the repeat state.
- 1000 ร 1.05 = โ 1050 (year 1)
- Press "=" again โ 1102.50 (year 2)
- Press "=" again โ 1157.625 (year 3)
- Press "=" again โ 1215.51 (year 4)
Press = twice to repeat the last operation. AC resets it.
Common mistakes (and how to avoid them)
A short field guide to the surprises that trip people up. Most of them are about precedence, percent context, or memory state.
These are the calculation gotchas we see most often. None of them are bugs โ the calculator is doing math correctly. They're just places where natural English doesn't match the math rules.
โ2 + 3 ร 4โ gives 14, not 20
โ100 + 10% โ 10%โ doesnโt give 100
AC vs MC
Pressing = chains
Decimals don't equal fractions exactly
Most "wrong" results are correct math + a misread of the rules. When in doubt, parenthesize.
Practice with the PEMDAS challenge
Twenty questions on order of operations, with a worked solution after every answer. The standalone challenge replaces the old in-guide quiz.
When you finish reading, head over to the PEMDAS Math Challenge to pressure-test what stuck. It runs as an exam-style quiz: one question per screen, no skipping, full solution on every pick. You will see exactly which rules trip you up.
Your score saves on this device only. Bail mid-attempt and it counts as an incomplete try; finish a run and it joins your "best" / "last" history. There is no timer.
Take the PEMDAS Challenge
20 questions, one per screen, with a worked solution after every answer. The fastest way to find out which precedence rules still trip you up.
A quick 20 questions catches the precedence gotchas faster than re-reading the guide.
Quick Reference
| Pattern | Meaning | Example |
|---|---|---|
| p% of base | (p/100) ร base | 10% of 200 = 20 |
| base + p% | base ร (1 + p/100) | 200 + 10% = 220 |
| base โ p% | base ร (1 โ p/100) | 200 โ 10% = 180 |
| base ร p% | base ร p/100 (literal) | 200 ร 10% = 20 |
| a + b ร c | b ร c first | 2 + 3 ร 4 = 14 |
| (a + b) ร c | parentheses first | (2 + 3) ร 4 = 20 |
| โn | "x where x ร x = n" | โ144 = 12 |
| โ(a + b) | evaluate inside first | โ(9 + 16) = 5 |
| M+ | add result to memory | 141.60 โ memory = 141.60 |
| MR | recall memory | MR รท 4 โ uses stored value |
| Ans | insert last = result | 7 โ Ans ร 2 = 14 |
| โ / โ | walk through history | Recall any past calc |
FAQs
Why does 200 + 10% become 220?
โพ
Why does 200 + 10% become 220?
โพBecause + makes the calculator interpret 10% as "10% OF the number on the left". 10% of 200 is 20, so 200 + 20 = 220. Same logic applies to subtraction: 200 โ 10% = 180.
Why does 200 ร 10% give 20 (not "10% increase of 200")?
โพ
Why does 200 ร 10% give 20 (not "10% increase of 200")?
โพWhen multiplying or dividing, the calculator treats % as a literal divide-by-100. So 200 ร 10% = 200 ร 0.1 = 20. There's no "implied base" the way + and โ do it. To increase by 10%, type 200 + 10% = 220.
Why does 2 + 3 ร 4 equal 14, not 20?
โพ
Why does 2 + 3 ร 4 equal 14, not 20?
โพOrder of operations (PEMDAS / BODMAS): multiplication happens before addition. It evaluates as 2 + (3 ร 4) = 2 + 12 = 14. To get 20, type (2 + 3) ร 4.
What's the difference between AC and MC?
โพ
What's the difference between AC and MC?
โพAC (All Clear) clears your expression and result. Memory keeps its value. MC (Memory Clear) does the opposite โ clears only memory; expression stays. Press both if you want a totally clean slate.
How is Ans different from MR?
โพ
How is Ans different from MR?
โพAns always pulls from the LAST = press. MR pulls from whatever you stored with M+ / Mโ. Ans updates automatically every time you press =; memory only changes when you explicitly add/subtract or clear.
What happens if I press = without finishing my expression?
โพ
What happens if I press = without finishing my expression?
โพIf the expression isn't valid (trailing operator, unbalanced parens, etc.), the calculator shows an error and doesn't commit anything to history. The cursor stays where it was so you can fix the input.
Why does pressing = again change the result?
โพ
Why does pressing = again change the result?
โพRepeat-= is a feature: after A op B, pressing = again applies "op B" to the new result. Useful for counting in steps or compounding. Press AC to reset that state.
How many calculations does history remember?
โพ
How many calculations does history remember?
โพUp to 20, most recent first. When you make the 21st, the oldest one drops off. Use M+ to keep important values aside if you don't want them to age out.
Can I use my keyboard?
โพ
Can I use my keyboard?
โพYes. Digits, operators (+ - * /), parens, decimal, and percent all work. Enter or = computes. โ / โ walk history. Backspace deletes. Esc exits fullscreen mode.
Why does the calculator switch to scientific notation for big numbers?
โพ
Why does the calculator switch to scientific notation for big numbers?
โพJavaScript (and every web calculator) loses exact-integer precision above 2โตยณ (about 9 quadrillion). For numbers beyond that, it shows magnitude as scientific notation (e.g., 9.65 ร 10ยฒยณ). Magnitude is reliable; the last few digits may round.
I want trig / logarithms / ฯ / e. Where do I go?
โพ
I want trig / logarithms / ฯ / e. Where do I go?
โพThose are scientific-calculator territory. The basic calculator is intentionally minimal. Try our scientific calculator for sin, cos, log, ln, ฯ, e, and powers.