Contrast is not average brightness
Choosing black or white text from a hex colour requires linearised sRGB luminance and a ratio—not an average of the three channel numbers.
- Colour Palette File Maker
- PNG to JPEG Converter
- Image to WebP Converter
Guides
Understand what each formula means, why it applies, and where its rules come from.
19 guides
Nothing here matches that.
Markdown is not one renderer
Core Markdown describes document structure, but generated heading ids, extensions and sanitisation belong to the renderer that eventually publishes it.
- Markdown Table of Contents Maker
- Text Diff Maker
- Text Line Sorter and Deduplicator
- Word and Character Counter
Pace is not effort, and a split sheet cannot make them equal
Pace is elapsed time per distance; effort is relative to the runner and conditions. Learn what an even split proves, what it cannot, and why rounded rows drift.
- Running Split Planner
- TDEE Calculator
- Date Difference Calculator
What a row means when JSON becomes CSV
JSON has objects and arrays; CSV has rows and columns. Learn which shapes convert honestly, where types disappear, and why a round trip is rarely identical.
- CSV to JSON Converter
- JSON to CSV Converter
- CSV Column Selector
- JSON Formatter
- +1 more
Sample peak is not loudness or true peak
Sample peak checks stored values, true peak estimates the waveform between them, and LUFS measures programme loudness. Learn which target an audio delivery needs.
- WAV Volume Adjuster
- WAV Audio File Inspector
- WAV Audio Trimmer
Why subtitle offset is not subtitle drift
A constant subtitle delay and a timing drift need different repairs. Learn how to measure two sync points, choose a shift or scale, and avoid making the end worse.
- Subtitle Time Shifter
- WAV Audio Trimmer
What a checksum proves, and what it does not
A hash tells you two files are identical. It cannot tell you a file is safe, unmodified by an attacker, or from who it claims. The difference matters.
- File Checksum: SHA-256 and SHA-1
- WAV Audio File Inspector
- WAV Audio Trimmer
A ZIP is a container before it is a compressor
Learn when ZIP storage is better than DEFLATE, why photos and video rarely shrink twice, what archive overhead contains, and what CRC-32 does not prove.
- ZIP File Creator
- File Checksum: SHA-256 and SHA-1
A month is not a duration, and other date traps
Why date arithmetic is harder than it looks — inclusive counting, daylight saving, months of different lengths, and timers that drift.
- Date Difference Calculator
- Pomodoro Timer
- Recurring Date Schedule Maker
Borrowing is compounding, seen from the other side
A mortgage, a personal loan and a savings account run one formula. Seeing it makes early payments, overpaying and APR obvious.
- Compound Interest Calculator
- Loan Repayment Calculator
- Mortgage Repayment Calculator
- Savings Goal Calculator
- +2 more
Why two word counters disagree about the same text
What counts as a word, where a line ends, and why the answer differs between tools. Unicode, line endings and the quoting rules that make CSV harder than it looks.
- Word and Character Counter
- Text Line Sorter and Deduplicator
- Case Converter
- CSV to JSON Converter
- +1 more
A number that goes up is not the same as getting richer
Nominal against real. Why a positive return can still be a loss, why the two rates divide rather than subtract, and what a target in today's money is worth later.
- Inflation Impact Calculator
- Compound Interest Calculator
- Savings Goal Calculator
Percentage change is not percentage points
Two different quantities that share a symbol, plus why a rise and a fall of the same percentage do not cancel out, and what lowest terms is actually for.
- Percentage Calculator
- Fraction Simplifier
- Profit Margin Calculator
How to print something at its true size
Why a 5 mm grid comes out 4.7 mm, what the CSS inch actually is, and the print settings that quietly rescale a page before it reaches the paper.
- Printable Graph Paper Planner
- Printable Month Calendar Planner
- Printable Ruled Paper Maker
What BMI actually measures, and what it cannot
A nineteenth-century population statistic used as a personal diagnosis. Where the formula comes from and where it fails.
- BMI Calculator
- TDEE Calculator
What is the VAT fraction, and why is it one sixth?
The share of a VAT-inclusive price that is tax, in lowest terms. Why authorities publish it, why 20% gives 1/6, and why most rates give nothing tidy.
- VAT Calculator
- UK VAT Calculator
- Irish VAT Calculator
- German VAT Calculator
What actually makes a password strong
Entropy, not complexity rules. Why a random four-word phrase beats a symbol-stuffed word, and why the source of randomness matters.
- Password Generator
- UUID Batch Generator
Why lossless images are sometimes smaller than lossy
Lossy is not automatically smaller. For flat colour, sharp edges and small images the lossless encoder often wins, and here is how to tell in advance.
- Image to WebP Converter
- PNG to JPEG Converter
- Image Resizer
- Image Metadata Remover
Zero-rated, exempt and reduced are three different things
Three ways a VAT system charges less than the standard rate, and only one of them is a rate. The difference decides whether a business can reclaim its input tax.
- UK VAT Calculator
- Irish VAT Calculator
- German VAT Calculator
- Austrian VAT Calculator
- +2 more