Why 2 + 3 × 4 comes to 20 here, not 14
Type 2, then +, then 3, then ×, then 4, then =, and this calculator answers 20. A scientific or graphing calculator, built to follow algebraic order of operations, answers 14 for the same key presses, because it waits to see the whole line before deciding that multiplication happens before addition. Neither calculator is broken. They are running two different, well-established rules, and knowing which one is in your hand matters.
This is called immediate execution, sometimes chain calculation: every operator key fires the operation that is already waiting as soon as you press the next one. Press +, the calculator remembers 2 and "add". Type 3, then press ×, and it does not wait, it immediately works out 2 + 3 = 5 there and then, and only after that does it start waiting on the ×. By the time you press =, the sum has already been walked through step by step, left to right, exactly in the order you pressed the keys.
This is not a quirk of cheap calculators. It is how every simple four-function calculator has worked since the first pocket models arrived in the 1970s, because building a chip that just applies the next operation as it arrives is far cheaper than one that parses a whole expression for precedence. Basic calculators, till machines and most phone calculator apps in their plain view all still work this way. If you need standard mathematical precedence, look for a calculator that says "scientific" and enters a full expression before evaluating it.
What the % key actually does
The percent key is the most misunderstood button on any calculator, because it quietly changes behaviour depending on which operator sits next to it. On this calculator, and on the vast majority of standard four-function calculators, it works two different ways:
After addition or subtraction, the percent key treats the number as a share of whatever total is already sitting in the calculator, so 200 + 10% adds ten percent of 200, which is 20, giving 220. That is the everyday "add the service charge" or "take off the discount" behaviour. After multiplication or division, or typed on its own, the percent key just divides the number by 100, so 200 × 10% is exactly the same sum as 200 × 0.1, giving 20. Both conventions are genuinely standard; the confusion comes from assuming a percent key always means the same thing, when it means "of this total" in one case and "as a plain fraction" in the other. Cheaper calculators occasionally skip this distinction altogether and always divide by 100, which is worth checking on any calculator before trusting a bill split or a discount to it.
MC, MR, M+ and M−: memory for a generation that skipped it
The four memory keys hold one running number completely separate from whatever is on the main display, which is useful whenever a calculation has more than one running part, like adding up several receipts while a subtotal builds quietly in the background.
Work out one receipt, press M+ to bank it, clear the display with C, work out the next receipt, press M+ again, and memory now holds both added together, ready to be pulled back with MR whenever you need the running total. The small "M" indicator lit up on the display is the only sign memory holds anything; it disappears the moment memory returns to zero or MC is pressed. Unlike the display itself, memory survives a plain C press, precisely so a slip on the current sum does not wipe out a running total you were keeping to one side.
Why 0.1 + 0.2 shows 0.3, and why very big numbers show an "e"
Computers store decimal numbers in binary, and most everyday decimals, 0.1 and 0.2 included, cannot be written exactly in binary any more than a third can be written exactly in decimal. Add them on a raw computer and you can get 0.30000000000000004 back, a real and famous artefact of floating-point arithmetic rather than a bug in any particular calculator. This calculator rounds every result to ten decimal places before it is shown, which is enough precision for any real calculation and quietly throws away that binary noise, so 0.1 + 0.2 reads as the plain 0.3 you expect.
The same rounding has a ceiling. Numbers larger than a trillion or smaller than a billionth switch to exponential notation, shown as a decimal figure and an "e" followed by the power of ten, the same trade-off a real calculator makes when it runs out of physical digit positions on its display. A basic calculator is built for everyday sums, not for astronomy or particle physics, so treat an "e" on the display as a sign to reach for a scientific calculator rather than as an error.
Pressing = again and again
Work out 2 + 3 = and the display reads 5. Press = a second time, with no new number typed, and it reads 8, because the calculator repeats the last operation, adding 3 again. Press = once more and it reads 11. This is deliberate: the calculator remembers the last operator and the last number you typed with it, and treats a bare = as "do that again to whatever is on the display now", which turns the = key into a quick way to add a fixed number repeatedly or to apply a fixed percentage rise several times over.
Questions people ask
Why does my phone give a different answer to 2 + 3 × 4 than this calculator?
Your phone's calculator app most likely switches to algebraic order of operations once you rotate it into its wider, scientific layout, while its plain portrait view often runs the same immediate-execution rule this calculator does. Check which mode produced the answer before assuming either one is wrong.
What is the difference between C and CE?
CE, clear entry, wipes only the number currently being typed, leaving any pending operator and running total untouched, so a mistyped second number can be corrected without losing the first. C, all clear, resets the entire calculation, including the pending operator, back to zero.
Does pressing C erase what is in memory?
No. Memory, set by M+ and M− and shown by the M indicator, is deliberately separate from the main calculation, so a plain C only clears the display and the current sum. Only MC clears memory itself.
Why does the display sometimes show an "e" instead of a full number?
The result is too large or too small to show as a plain decimal within this calculator's digit budget, so it switches to exponential notation, a number multiplied by a power of ten. It is a display limit, not an error in the sum itself.
Can I divide by zero?
No calculator can; division by zero is undefined in ordinary arithmetic. This one shows "Cannot divide by zero" and waits for C before it accepts another sum, rather than guessing at an answer.
Does the percent key work the same on every calculator?
Not quite. This calculator uses the common convention described above, where % after + or − scales to the running total. Some simple calculators always divide by 100 regardless of the operator, which gives a different answer for additions and subtractions, so it is worth testing an unfamiliar calculator's % key with a known sum like 200 + 10% before relying on it.
What does the ± key do?
It flips the sign of the number currently on the display, turning 5 into −5 or back again, without needing a separate subtraction. It works on whatever number is showing, whether that is mid-entry or a finished result.
This calculator rounds display results to ten decimal places and switches to exponential notation past roughly a trillion or a billionth; for expressions that need standard algebraic precedence, scientific notation, or built-in functions, use a scientific calculator instead.