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, binary arithmetic, a chain of…
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.
Calculator Rules for the SAT, ACT, GRE, GMAT and MCAT
Every major exam has its own calculator policy and they disagree with each other. Here is what each one currently allows, and what gets confiscated a…
How to Build a Calculator in JavaScript
A working browser calculator in about a hundred lines, and the operator-precedence problem that breaks almost every first attempt.
How to Build a Calculator in Python (Without eval)
Start with a command-line calculator, then replace the dangerous eval() with a small expression parser you actually control.
What Is a Calculator? Definition, Types and Button Meanings
A precise definition, the six families of calculator in use today, and the button labels that confuse people most.
Percentages Explained: Every Formula You Actually Need
Five formulas cover almost every percentage question anyone actually asks. Here they are, with the traps that make each one go wrong.
Compound Interest: The Formula, the Intuition and the Traps
Why balances curve upward instead of rising in a straight line, what compounding frequency actually changes, and the shortcut worth memorising.
How Mortgage Interest Is Actually Calculated
Why your first years are almost all interest, where the standard payment formula comes from, and what an extra $100 a month really removes.
BMI: What the Number Means and Where It Fails
Where BMI came from, why clinicians still use a 190-year-old formula, and the four groups it routinely misclassifies.
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 a fortnight, and the signs you have cut too far.
Standard Deviation and Variance: What Spread Really Tells You
Why we square the deviations, when to divide by n−1, and how to read a standard deviation without over-interpreting it.