How a Calculator Works: From Key Press to Answer
Press a key and the answer appears before your finger leaves the button. Between those two moments sit a keypad matrix, a binary number system, a cha…
Calculator guides and explainers
The reasoning behind the numbers: how the formulas work, where they come from, and where they stop being true.
Before Calculators: How People Did the Maths by Hand
Slide rules, log tables, mechanical adders and rooms full of human computers carried engineering, navigation and finance for three centuries. Here is…
Calculator Rules for the SAT, ACT, GRE, GMAT, MCAT and More
Every major exam has its own calculator policy, and they disagree with each other. This is the current position for each test: whether a calculator i…
How to Build a Calculator in JavaScript
A working browser calculator in about a hundred lines: the markup, the state model, keyboard handling, and the operator precedence problem that trips…
How to Build a Calculator in Python
Start with a command-line calculator, then replace the dangerous eval() call with a small expression parser you control. Includes the shunting-yard a…
What Is a Calculator? Definition, Types and Terminology
A precise definition, the families of calculator in use today — four-function, scientific, graphing, financial, programmable — and the button labels …
Calculator History and Memory: Viewing, Saving and Clearing Past Results
Which calculators keep a running history, how to bring it back on Windows, iPhone, Android and Casio models, and how to clear it when you are handing…
Percentages Explained: Every Formula You Actually Need
Percent of a number, percent change, reverse percentages, percentage points and the discount stacking rule. Five formulas cover almost every percenta…
Compound Interest: The Formula, the Intuition and the Traps
Why balances curve upward instead of rising in a straight line, what compounding frequency really changes (less than you think), and the rule of 72 s…
How Mortgage Interest Is Actually Calculated
Amortization in plain English: why the first years are almost all interest, what an extra $100 a month really removes, and where the standard payment…
BMI: What the Number Means and Where It Fails
Where BMI came from, why clinicians still use it despite its flaws, and the four groups it routinely misclassifies — athletes, older adults, very tal…
Calorie Deficit: How to Set One You Can Actually Keep
How to size a deficit against your own maintenance level, why the scale lies for the first fortnight, and the signals that mean you have cut too far.