Calculator

Order of operations (PEMDAS/BODMAS) and why it bites

A calculator that respects order of operations evaluates 2 + 3 x 4 as 14, not 20, because multiplication binds tighter than addition. The mnemonic is PEMDAS in the US (Parentheses, Exponents, Multiplication/Division, Addition/Subtraction) and BODMAS/BIDMAS elsewhere — same rules, different acronym. The two pitfalls people hit are that multiplication and division share a rank and are evaluated left to right (so 8 / 2 x 2 is 8, not 2), and likewise addition and subtraction. When in doubt, add parentheses: they cost nothing and remove all ambiguity.

This is also why a simple 'add as you go' adding-machine — where each operator acts immediately on the running total — gives a different answer from an expression calculator for the very same keystrokes. Know which kind you're using. SnapToolz evaluates the whole expression with correct precedence, so what you'd write on paper is what you get.

Floating-point quirks: when 0.1 + 0.2 isn't 0.3

Type 0.1 + 0.2 into almost any computer and the raw result is 0.30000000000000004. This isn't a bug in the calculator — it's a consequence of how computers store decimals. Numbers are held in binary floating point (the IEEE 754 standard), and just as one third can't be written exactly as a finite decimal, 0.1 and 0.2 can't be written exactly in binary. The tiny rounding error is real and it's everywhere; most tools simply hide it by rounding the display.

Where this actually matters is money and equality checks. Summing a long column of currency values in floating point can leave you a cent off, and testing whether two computed values are 'exactly equal' can fail when they look identical on screen. The defence is to round to the precision you care about (two decimals for currency) at the end, and to never trust a bare equality test on computed decimals.

When a calculator is the wrong tool

• Repeating the same formula over many rows of data — totals, averages, tax on a list of prices — belongs in a spreadsheet, where the formula lives once and recalculates as data changes. Open the built-in Spreadsheet for that.
• Loan repayments, EMIs and amortisation have a specific compounding formula that's easy to get wrong by hand; use the Loan / EMI Calculator and the math is explained in the EMI loan math guide.
• Splitting a restaurant bill with tip and a headcount is faster on the dedicated Tip Calculator.
• Converting between units (miles to km, Fahrenheit to Celsius, GB to MB) is a conversion, not a calculation — reach for a unit converter so you're not hard-coding factors.