General
Two calculators. The only real question is which keyboard you want in front of you, and that is decided by whether you are pressing one key at a time or typing a whole expression out.
2 tools in General
Why there are two of these rather than one
A four-function calculator and a scientific calculator are not the same instrument with more buttons. They read what you type in genuinely different ways, and mixing the two behaviours in one tool is how calculators end up giving answers people cannot reproduce.
The plain calculator works the way a desk calculator does: each key press acts on the running total immediately, so pressing 2 + 3 × 4 gives 20, because the 3 was added the moment the × arrived. The scientific one parses the whole expression before evaluating any of it, so the same keys give 14, because multiplication binds tighter than addition. Both answers are correct for the machine that produced them. Neither is a bug.
- Calculator
- You are adding a column of figures, or doing one operation at a time and want to see the total move as you go.
- Scientific Calculator
- You have an expression with brackets, powers, roots, logs or trigonometry in it, and you want it evaluated the way it is written.
What both of them refuse to do
Neither one evaluates what you type as code. Expression input is parsed by a small arithmetic reader that understands numbers, brackets, the operators, a factorial, pi and e, and a fixed list of single-argument functions — and throws on anything else. That is a deliberate choice over the one-line alternative every JavaScript calculator is tempted by, which would happily run whatever a pasted string turned out to contain.
Both also trim the artefacts binary floating point leaves behind, so 0.1 + 0.2 reads as 0.3 rather than as 0.30000000000000004, without rounding away digits you actually typed. And in degree mode the scientific calculator snaps values that should be exactly zero to zero, because a sine of 180 reading 1.22e-16 is technically honest and practically useless.
Two calculators, two answers
Why do the two calculators disagree about 2 + 3 × 4?
Because they read the keys differently and both are right for what they are. The plain one acts on each key as it arrives, so the 3 has already been added by the time the multiplication sign appears and the answer is 20. The scientific one reads the whole expression first and applies operator precedence, so the answer is 14. If you want precedence, use the scientific one or put brackets in.
Can I type instead of clicking the buttons?
Yes. On the plain calculator the number keys, the four operator keys, a full stop or comma for the decimal point, Enter or equals to evaluate, Backspace to delete a digit and Escape to clear all work straight from the keyboard. The scientific calculator takes an expression as text, so you can type or paste the whole thing and press Enter.