Basic Calculator

Step by step

1. Tap the number keys — or just type on your keyboard. Digits, ., + − * / and Enter all work.
2. Press an operator to finish the sum before it. Chaining works the way a desk calculator does: 5 + 3 × 2 gives 16, because pressing × settles 5 + 3 first.
3. Press = to finish. The completed line drops onto the paper tape on the right.
4. Tap any line on the tape to pull that answer back into the display and keep working with it.
5. AC clears everything, CE clears only the number you are typing, and the arrow key rubs out one digit.
6. Use M+ and M− to add the display into memory, MR to recall it, MC to wipe it. An M shows above the keypad while memory holds anything.

Good to know

• The % key follows the shop-till convention: 200 + 10 % gives 220, because after + or − the percentage is taken of the running total. On its own it just divides by 100.
• Answers are kept to 12 significant figures, which is why 0.1 + 0.2 shows 0.3 here instead of the 0.30000000000000004 a raw computer answer would give.
• Dividing by zero shows “Cannot do that” rather than a number — nothing is silently wrong.
• The tape holds the last 60 lines and copies out as plain text, which is handy for pasting into a message or a receipt.
• Need brackets, powers or trig? The Scientific Calculator reads a whole expression at once, including ( and ).

The maths behind it

• Immediate execution a op b = result result becomes the new a Each operator key settles the sum to its left, then waits for the next number. This is the model desk and pocket calculators use — not algebraic precedence.
• Percent after + or − a + b % → a + (a × b ÷ 100) So a $200 bill plus 10% is 220, not 200.1.
• Rounding for display shown = round to 12 significant figures Binary floating point cannot store 0.1 exactly. Rounding at 12 figures hides that artefact while leaving every digit you actually entered intact.