📚 Trivia Collection
Every tool on this site comes with a "Side Note" section — trivia or background knowledge beyond the calculator itself. Follow your curiosity from topic to topic, Wikipedia-style.
Crypto
- Side Note — The Most-Hacked Passwords in the World
- Side Note — How "correct horse battery staple" changed the conversation
- Side Note — Why Two-Factor Codes Settled on 6 Digits
- Side Note — The Inventor of MD5 and the Trajectory of a "Broken" Algorithm
- Side Note — SHAttered: A Collision Attack 9.2 Quintillion Operations in the Making
- Side Note — Bitcoin Mining and the Astronomical Scale of SHA-256 Computation
- Side Note — Why "512 Bits"? Bit Length and the Meaning of Security
- Side Note — The Birth of Keccak and the NIST Competition: Five Years to Crown the Next Standard
- Side Note — The Password Hashing Competition and the Origins of Argon2
- Side Note — Why Comparing Hashes Is Enough to Verify a Password
- Side Note — Why Different Hash Functions Suit Different Purposes
- Side Note — Why Official Sites Publish Hash Values
- Side Note — Why a hash value alone can't pin down the algorithm
- Side Note — The Battle of Passwords and Hashes: Why BCrypt Is Chosen
- Side Note — Behind Authentication: What Those Few Hundred Milliseconds on Login Are
- Side Note — why it's named after Caesar
- Side Note — The Story of Enigma and Bletchley Park
- Side Note — How the Kasiski Examination Broke an "Unbreakable" Cipher
Developer Tools
- Side Note — Why 128 Bits?
- Side Note — Why Nano ID Can Be Shorter Than a UUID
- Side Note — How ULID Brought Chronological Order to the World of IDs
- Side Note — How UUID v7 Brought Time Back to the UUID Family
- Side Note — Giving UUIDs a built-in clock
- Side Note — Why JSON Won Over XML
- Side Note — 50 Years of SQL: A History of Relational Databases
- Side Note — Why did URLs end up with so many tracking parameters?
- Side Note — Why Was the "One Record per Line" Format Invented?
- Side Note — The "Type Drift" Problem That Type-Inference Tools Solve
- Side Note — Why Go Pairs Structs With json Tags
- Side Note — XML, the offspring of SGML
- Side Note — Why YAML Became the Go-To Config Format
- Side Note — Why TOML became the common language of config files
- Side Note — Why config files are written in YAML but tools want JSON
- Side Note — The Reverse of JSON to Go Struct Conversion
- Side Note — How key matching differs between CSV diff and JSON diff
- Side Note — Why there's no single "correct" way to turn XML into JSON
- Side Note — What to watch for when converting JSON back into XML
- Side Note — The Surprising History of CSV: 40 Years Without a Standard
- Side Note — The Origin of JSON: "Discovered", Not Invented
- Side Note — Why APIs prefer JSON over CSV
- Side Note — Why bundled INSERT statements are faster
- Side Note — Why Markdown tables need nothing but pipes and hyphens
- Side Note — what actually differs between a Markdown table and a CSV
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Side Note — Why the
<table>tag refuses to die - Side Note — Why does a browser's "table copy" include HTML?
- Side Note — Why XML Came to Be Called "Verbose"
- Side Note — Why Does Excel "Break" CSV Data?
- Side Note — Why CSV Went So Long Without an Official Standard
- Side Note — Why a text diff alone isn't enough for CSV files
- Side Note — Why SOAP and XML are still around
- Side Note — Why JSON Lines became the common language of ML and log processing
- Side Note — Base64, Email, and the URL Collision
- Side Note — Why ASCII is 7-Bit
- Side Note — The 80-Character Curse: A Tradition from Punch Cards
- Side Note — The "Character Reference" Mechanism Inherited from SGML
- Side Note — Why "縺薙繧薙?縺ｫ縺｡縺ｯ" became the face of Japanese mojibake
- Side Note — How mismatched line endings cause invisible bugs
- Side Note — Why X Counts Characters with "Weights"
- Side Note — How JWTs Make "Stateless Authentication" Possible
- Side Note — Why JWT Signing Can Be Done Entirely in the Browser
- Side Note — HMAC vs. public-key signatures: what is the difference?
- Side Note — why "KiB" was born in 1998
- Side Note — Why Do Computers Run on Binary?
- Side Note — The Curious Properties of XOR
- Side Note — The hidden relationship between social media character limits and byte counts
- Side Note — Why Basic Auth survives despite its age
- Side Note — Why CSP exists: escaping alone was never enough to stop XSS
- Side Note — securityheaders.com and the history of clickjacking defense
- Side Note — The Birth of robots.txt: The Day the Internet Got Manners
- Side Note — The Day Search Engines Agreed on One Sitemap Format
- Side Note — Why OGP exists — Facebook built it to make the "Like" button work
- Side Note — Why JSON-LD replaced Microdata and RDFa
- Side Note — Why ads.txt exists: an industry standard against ad inventory "spoofing"
- Side Note — Why hreflang so often seems to "not work"
- Side Note — How the Web App Manifest relates to PWAs
- Side Note — robots.txt vs. the robots meta tag: a division of labor between crawling and indexing
- Side Note — The origin of security.txt — the "first point of contact" that bug bounties alone couldn't provide
- Side Note — The Luhn Algorithm — The Guardian of Card Numbers Since 1954
- Side Note — Hans Peter Luhn, the Father of the Check Digit
- Side Note — Where "Valid" Ends and "Corrupt" Begins
- Side Note — What happens inside a regex engine
- Side Note — how LCS (Longest Common Subsequence) powers text diffing
- Side Note — Comparing lists with set operations
- Side Note — Why a file's true identity is in its bytes, not its extension
- Side Note — Why do computers count time in seconds?
- Side Note — Why computers use two's complement
- Side Note — How IEEE 754 became a common language
- Side Note — Why does the computing world have a dedicated format for "durations"?
- Side Note — Why machine learning wanted a "less precise" number format
- Side Note — Where MIME types came from
- Side Note — Slugs and the kebab-case debate
- Side Note — How Unicode unified a fragmented world of character encodings
- Side Note — Why Base64 Makes Files 33% Larger
- Side Note — Why testing needs "seeded" dummy data
- Side Note — Why is it called ".htaccess"?
- Side Note — Half a Century of Cron
- Side Note — Why Writing a Cron Expression Is Harder Than Reading One
- Side Note — From Cron to systemd Timers
- Side Note — What it means to convert a systemd timer back to cron
Text
- Why Preview Before Publishing?
- Side Note — Where the 140-character limit came from
- Side Note — "Sumomo mo Momo mo Momo no Uchi" and the Difficulty of Word Segmentation
- Side Note — Why Different Programming Languages Ended Up With Different Naming Conventions
- Side Note — Why Japanese groups numbers by 万 (10,000)
- Side Note — Why Do Kanji Have Both On'yomi and Kun'yomi Readings?
- Side Note — Emoji Origins and Unicode
- Side Note — How "ojisan kobun" became an internet meme
- Side Note — How "gyaru-go" has kept reinventing itself
- Side Note — Why Uchinaguchi Counts as its Own Language
- Side Note — how a math notation block became a social media decoration
- Side Note — A Brief History of ASCII Art
- Side Note — The Telegraph Era That Gave Us Morse Code
- Side Note — the art of decoding by ear
- Side Note — The 'reading' skill flag semaphore trained
- Side Note — The 'reading' skill flag semaphore trained
- Side Note — Why 貴社 Sounds Awkward When Spoken Aloud
- Side Note — Where "Alpha, Bravo, Charlie" Came From
- Side Note — The Birth of the QR Code and How It Works
Math
- Side Note — History of the Calculator: From a 30-Ton Monster to the Smartphone
- Note — Japan's Consumption Tax History: 35 Years of Change
- Note — The Illusion That "One Free" Beats "Half Price"
- Note — The Limits of BMI and the "Overweight Paradox"
- Note — Is Compound Interest "Humanity's Greatest Invention"?
- Side Note — Why the 4-digit vs 3-digit gap exists
- Side Note — Why Computers Struggle With Really Big Numbers
- Side Note — What actually separates a "scientific" calculator from a regular one
- Side Note — Ancient Egypt's curious 'unit fractions'
- Side Note — Why is the factorial symbol an exclamation mark?
- Side Note — When was the term "standard deviation" coined?
- Side Note — Where Did the GPA System Come From?
- Side Note — Where Did Map Scales Come From?
- Side Note — The stories behind the meter and the degree Fahrenheit
- Side Note — The history behind tsubo, tatami mats, and the acre
- Side Note — why shoe sizing is such a mess across countries
- Side Note — why ring sizing differs so much from country to country
- Side Note — How did 号, S/M/L, and US/UK/EU sizes come to be?
- Side Note — Why a Linear Function Is Called "Linear"
- Side Note — The Origin of the Word "Parabola"
- Side Note — The Rivalry Behind the Cubic Formula
- Side Note — Compound interest and the number e
- Side Note — Logarithms in decibels and earthquake magnitude
- Side Note — Ellipses in planetary orbits
- Side Note — Hyperbolas and navigation
- Side Note — Why do experts dislike pie charts?
- Side Note — Gauss and the legend of 1 to 100
- Side Note — Geometric growth and the paper-folding myth
- Side Note — Fibonacci, the golden ratio, and Binet's formula
- Side Note — The Pythagoreans and the "mystery of numbers" found in figurate numbers
- Side Note — Why prime numbers matter
- Side Note — Why a 2,000-year-old algorithm is still in use
- Side Note — RSA encryption and the hardness of factorization
- Side Note — why a 2,000-year-old algorithm is still in daily use
- Side Note — The "Clock Arithmetic" Behind Modern Cryptography
- Side Note — From a 3rd-century arithmetic text to speeding up RSA encryption
- Side Note — The 18th-century function that counts what's coprime
- Side Note — Why SSS, SAS, and ASA are enough to "fix" a triangle
- Side Note — Why a circle's area is "π times radius squared"
- Side Note — Why the "shortest path" doesn't look like a straight line
- Side Note — the cylinder-and-sphere relationship Archimedes had carved on his tombstone
- Side Note — Vectors were born out of Hamilton's quaternions
- Side Note — The World's Steepest Streets and Railways
- Side Note — The chickens and rabbits problem has roots in an ancient Chinese text
Date/Time
- Side Note — Humanity's Quest for Precision — Atomic Clocks and Leap Seconds
- Side Note — World Speed Records — Various Speeds Measured with a Stopwatch
- Side Note — The Pomodoro Technique and the Story Behind Its 25-Minute Interval
- Side Note — The World's Unusual Timezones — Countries with 30- and 45-Minute Offsets
- UTC vs GMT vs BST: Why World Time Differences Change
- Side Note — Why 25 minutes? The origin of the Pomodoro Technique
- Side Note — Japan's Public Holidays vs. the World — Many Holidays, Few Paid Vacations Taken
- Side Note — The Surprising History of "National Holidays" and Substitute Holidays
- Side Note — The Mystery of Rokuyou — No Scientific Basis, Yet 60–70% Consult It
- Side Note — History of Japanese Era Names — A 1,400-Year Tradition Unique to Japan
- Side Note — The History of Japan's Era Name System
- Side Note - Why "Kanreki" Lines Up With the Zodiac
- Side Note — the origin of the 12 zodiac animals
- Side Note — When Did Japanese Name Numerology Begin?
- Side Note — the "Bell of the Hours" and Edo's sense of time
- Side Note — the uniquely Japanese custom of seasonal greetings
- Side Note — Ways of Counting Age Around the World
- Side Note — The Surprising Origin of Yakudoshi
- Side Note — Why April 1 Birthdays Are One Year Ahead
- Side Note — Why one day can change your school grade in Japan
- Side Note — the colors and origins of Japanese longevity celebrations
- Side Note — where the "kaiki" counting comes from
- Side Note — how long has the mochu hagaki custom been around?
- Side Note — since when has "half-return" been the standard?
- Side Note — why does ofuse have a "going rate" at all?
- Side Note — why are the digits 4 and 9 avoided in koden amounts?
- Side Note — why are even numbers avoided in goshugi amounts?
- Side Note — why do shussan-iwai and goshugi follow different etiquette?
- Side Note — the surprising pitfalls of counting days by hand
- Side Note — when "14 days later" is defined by law
- Side Note — Why time still runs on base 60, not base 10
- Side Note — There Is No Legal Definition of a "Business Day"
- Side Note — countdowns and humanity's culture of waiting
- Side Note — Why Thursday Decides the Week Number
Design
- Side Note — The Mystery of Color: The Human Eye and 16.7 Million Colors
- Side Note — the history behind these color models
- Side Note — The Origins of Accessibility Standards
- Side Note — The history of color vision testing and the Ishihara test
- Side Note — Why designers avoid picking colors "by feel"
- Side Note — The work of finding brand colors from photos
- Side Note — The origins of alpha blending
- Side Note — The challenge of drawing on sixteen pixels
- Side Note — Why CSS Gradients Replaced Gradient Images
- Side Note — how box-shadow changed what the web could express
- Side Note — How Flexbox Changed CSS Layout History
- Side Note — CSS Grid's Pursuit of a "Second Dimension" That Flexbox Doesn't Cover
- Side Note — The Long Road to Standardizing position: sticky
- Side Note — How rem Made It Into the CSS Spec
- Side Note — How aspect ratio standards came to be
- Side Note — the culture of placeholder images
- Side Note — how JPEG exploits the weaknesses of human sight
- Side Note — why was WebP created?
- Side Note — Why HEIC so often refuses to open
- Side Note — Why AVIF was built to be royalty-free from the start
- Side Note — Which hides better, mosaic or blur?
- Side Note — Why are profile pictures usually square?
- Side Note — The Tradition of the Contact Sheet
- Side Note — where the word "pixel" comes from
- Side Note — A brief history of chroma key compositing
- Side Note — the paper size born from the square root of two
- Side Note — Why "Lorem Ipsum" Refuses to Go Out of Style
- Side Note — Where the seal came from
Network
- Side Note — The Birth of the URL: Tim Berners-Lee and the Dawn of the World Wide Web
- Side Note — The Birth of REST: How Roy Fielding's Dissertation Changed Web Development
- Side Note — A Brief History of HTTP Status Codes
- Side Note — The curl Exit Code System
- Side Note — Why curl Is the Tool Everyone Uses but Almost No One Knows
- Side Note — Why is internet speed always quoted in bits?
- Side Note — Why do port numbers only go up to 65535?
- Side Note — why email validation happens in two stages
- Side Note — How the three pillars of anti-spoofing email defense came to be
- Side Note — the history behind DNS records and email authentication
- Side Note — nobody actually "broadcasts" DNS changes
- Side Note — Why DNS needed a way to stop spoofing
- Side Note — Why STARTTLS wasn't enough, and how MTA-STS came about
- Side Note — Protecting mail encryption with certificates, not just "don't eavesdrop"
- Side Note — The "silent failure" gap that TLS-RPT closed
- Side Note — How DMARC reports turned an invisible problem visible
- Side Note — How public-key cryptography stops email impersonation
- Side Note — Email headers are a stack of digital postmarks
- Side Note — The IPv4 Exhaustion Problem: The Day 4.3 Billion Addresses Ran Out
- Side Note — IPv4 address exhaustion and the birth of CIDR
- Side Note — IP Address Trivia: 8.8.8.8 and the End of IPv4
- Side Note — WHOIS history and the GDPR turning point
- Side Note — blacklists piggyback on the DNS system itself
- Side Note — The algorithm behind IP range to CIDR conversion
- Side Note — Why "Private" IP Addresses Cannot Reach the Internet
- Side Note — Why IPv6 Doesn't Use "Subnet Masks"
- Side Note — Why CIDR Blocks Can Never "Partially" Overlap
- Side Note — The History of Domain Names and the Birth of WHOIS
- Side Note — Behind the Scenes of How "Cat" and "日本語" Became Domain Names
- Side Note — Why domain name validation keeps getting reinvented
- Side Note — A brief history of SSL/TLS certificates and certificate authorities
- Side Note — The evolution of TLS versions and their vulnerabilities
Money
- Side Note — Why take-home pay in Japan is typically 75–85% of gross
- Side Note — why is the gap between gross and net pay so large in Germany?
- Side Note — why is the gap between gross and net pay so large in France?
- Side Note — why does the UK tax salary and National Insurance separately?
- Side Note — Why don't the self-employed pay Class 2 National Insurance any more?
- Side Note — Why is "low salary plus dividends" such a common UK tax strategy?
- Side Note — why are federal income tax and FICA withheld separately in the US?
- Side Note — Why does my bonus get taxed differently than my paycheck?
- Side Note — Why does self-employment tax look double the employee rate?
- Side Note — why does IRPF vary so much between Spanish regions?
- Side Note — Italy's "13th salary" and its patchwork of local taxes
- Side Note — The freelancer's "social insurance wall"
- Side Note — Where Does the Term "Gross-Up" Come From?
- Side Note — Why Japanese Bonuses Are Legally a "Discretionary Payment"
- Side Note — Why does the premium rate change at 60 hours a month?
- Side Note — Why the odd "6 months, then every year" grant cycle?
- Side Note — Why Is It Called "Hometown Tax"?
- Side Note — What's the hourly rate for a ¥10M annual salary?
- Side Note — Why "deviation scores" are used for income, not just exams
- Side Note — Why is the maternity allowance rate exactly two-thirds?
- Side Note — Why the sickness and maternity allowances share the same two-thirds rate
- Side Note — Why the out-of-pocket limit uses a "fixed amount plus 1%" design
- Side Note — Why the medical expense deduction has two different thresholds
- Side Note — The medical cost containment goal behind the Self-Medication Tax System
- Side Note — Why Japan started recognizing "employee expenses"
- Side Note — Why the life insurance premium deduction split into "new" and "old" systems
- Side Note — How the earthquake insurance premium deduction came to be
- Side Note — Why it's called a "benefit," not a "leave allowance"
- Side Note — Freelancers building their own retirement fund
- Side Note — Why severance pay gets preferential tax treatment
- Side Note — why are there so many "walls"?
- Side Note — The Mystery of the "35-Year" Home Loan
- Why a lower mortgage payment does not always mean a cheaper loan
- Side Note — Watch for HELOC "payment shock"
- Side Note — Two Ways to Turn Home Equity Into Cash
- Side Note — Understanding the "Second Mortgage"
- Side Note — Same Collateral, Two Different Repayment Shapes
- Side Note — Why DTI became such a central lending metric
- Side Note — What you can borrow isn't always what you should borrow
- Side Note — where the idea of tracking your net worth came from
- Side Note — Why Equal Principal Repayment Costs Less in Interest
- Side Note — Where the Names "Snowball" and "Avalanche" Came From
- Side Note — How auto loans differ from mortgages
- Side Note — Leasing a Car Means Using It, Not Owning It
- Side Note — Buy vs Lease: Whether an Asset Remains in Your Hands
- Side Note — Why a "new" car becomes "used" the moment you drive it off the lot
- Side Note — What you can borrow vs. what you should keep
- Side Note — Why the sticker price is rarely the full story
- Side Note — Why the "Rent vs Buy" Debate Never Really Settles
- Side Note — Why Compound Interest Was Called "the Eighth Wonder of the World"
- Side Note -- Why CD Rates and Savings Rates Move Differently
- Side Note -- Why a Money Market Account Isn't a Money Market Fund
- Side Note -- Why Ladders Became Popular When Rates Started Moving Again
- Side Note -- Why T-Bills Became a Mainstream Savings Option Again
- Side Note — Where the Name "NISA" Comes From, and How the New System Differs
- Side Note — The Rule of 72 and the Mystery of Compound Interest
- Side Note -- Why the One-Year Mark Matters So Much
- Side Note — The People Behind Technical Indicators
- Side Note — Hyperinflation and the History of Money
- Side Note — The "¥20 Million Shortfall" Debate
- Side Note — Where Does the Name "401(k)" Come From?
- Side Note — The IRA was born in 1974, alongside a landmark pension law
- Side Note — The complexity hiding behind a "simplified" plan
- Side Note — A huge tax shelter built for one
- Side Note — A Legal Loophole Called the "Back Door"
- Side Note — Why "Mega"?
- Why the December 31 Balance Matters
- Side Note — Where did the idea of Coast FIRE come from?
- Side Note — Where does the name "Barista FIRE" come from?
- Side Note — The "shockingly simple math" behind savings rate and retirement
- Side Note — The Hidden Gap Between Gross and Net Yield
- Side Note — Why the "Total Inheritance Tax" Starts From Statutory Shares
- Side Note — Why the Gift Add-Back Period Grew From 3 Years to 7
- Side Note — Why It's Called a "Settlement"
- Side Note — Why Life Insurance Alone Gets This "Deemed Inherited Property" Treatment
- Side Note — Where Does the Idea of "Insurance Needs" Come From?
- Side Note — Why Is Income Protection Insurance Cheaper Than Term Life?
- Side Note — Why "Winning" at the First Inheritance Can Mean Losing at the Second
- Side Note — Why Such a Large Reduction Is Allowed for "Small-Scale" Land
- Side Note — Why the Formula Is "100,000 Yen x Number of Years"
- Side Note — Why Does the "Within 10 Years" Limit Exist?
- Side Note — Why Is the Same Property Taxed Twice?
- Side Note — Why Are Only First-Degree Blood Relatives Exempt?
- Side Note — What's the Difference Between "Contribution Share" and "Special Contribution Payment"?
- Side Note — Why the spousal residence right helps with the second inheritance
- Side Note — The history behind how the counting rules for forced heirship came to be consolidated in "Article 1044"
- Side Note — Why the claim was renamed from a "reduction claim" to a "forced heirship claim"
- Side Note — Why "bequests first, then the newest gifts" became the rule
- Side Note — Why does the "advancement" rule exist at all?
- Side Note — Why a contribution share is deducted upfront
- Side Note — When special benefits and a contribution share become an issue at the same time
- Side Note — What happens when someone already received too much?
- Side Note — The Surprising Ranking of Costly Home Appliances
- Side Note — Car Maintenance as a "Hidden Cost"
- Side Note — Why older cars are taxed more
- Side Note — Why registration and deregistration count months differently
- Side Note — From Automobile Acquisition Tax to Environmental Performance Tax
- Side Note — Why CALI insurance is mandatory
- Side Note — Why the vehicle weight tax is based on weight
- Side Note — Why Japan created the automobile recycling fee
- Side Note — Why shaken renews every two years
- Side Note — EV Value Goes Beyond Just "Breaking Even"
- Side Note — Why is the kei car limit set at 660cc?
- Side Note — The grade system looks mainly at claim count, not claim size
- Side Note — Why People Say "Claiming Small Accidents Isn't Worth It"
- Side Note — The second-car discount is an insurer rule, not an industry-wide system
- Side Note — The age condition needs revisiting every time your family situation changes
- Side Note — The driver scope rider is about honestly telling your insurer who actually drives
- Side Note — The deductible reflects a "small accidents on you, big accidents on insurance" mindset
- Side Note — Telematics insurance reflects how you actually drive in your premium
- Side Note — The premium gap reflects who supports the paperwork, not the coverage itself
- Side Note — the paperless discount is a small mirror of the insurance industry's digital shift
- Side Note — usage purpose is a yardstick for accident risk, not just premium math
- Side Note — Don't Overlook the Hidden Costs of Commuting
- Side Note — Why Water Bills Use a "Two-Part Tariff"
- Side Note — What Separates City Gas from Propane: Pipeline Infrastructure
- Side Note — Why "percent" and "percentage points" are different
- Side Note — The economist behind the 50/30/20 rule
- Side Note — why the fee rates differ so much between services
- Side Note — Why reselling profit is easy to misjudge one sale at a time
- Side Note — Why VAT was invented
- Side Note — the check digit hidden inside a VAT number
- Side Note — The Origin of "Warikan" and "Going Dutch"
- Side Note — Why Is the Lottery's Payout Ratio So Low?
- Side Note — Pari-mutuel vs. Fixed Payout
- Side Note — Why Winnings Are Tax-Free but Sharing Them Isn't
Business
- Side Note — Why a Profitable ROAS Can Still Mean Losses
- Side Note — Why a Simple Average Fails to Represent Project Progress
- Side Note — Why NPS Is Just a Simple Subtraction
- Side Note — Why eNPS Became the Employee Version of NPS
- Side Note — Where the Turnover Rate Metric Came From
- Side Note — How Cost per Hire Became a Standardized Metric
- Side Note — Time to Hire vs. Time to Fill
- Side Note — Why Measuring "Quality of Hire" Is So Difficult
- Side Note — Why Offer Acceptance Rate Is Called the "Last Gate" of Hiring
- Side Note — Where the Idea of a "Hiring Funnel" Comes From
- Side Note — The "First 90 Days" Wall in Early Employee Turnover
- Side Note — Absenteeism and the Hidden Cost of "Presenteeism"
- Side Note — Paid Leave Utilization and a "Hard to Take Time Off" Culture
- Side Note — The "karoshi line" and Japan's overtime cap regulation
- Side Note — Why CSAT Only Asks About the Most Recent Experience
- Side Note — Why "Reduce Effort" Beats "Delight the Customer"
- Side Note — How Gross Margin Differs From Operating Margin
- Side Note — Why operating margin reflects your core business strength
- Side Note — Why ordinary income margin reflects a company's true strength
- Side Note — Why net profit margin reflects a company's ultimate earning power
- Side Note — why businesses rely on break-even analysis
- Side Note — Why Book Value Stops at a Nominal Amount Instead of Zero
- Side Note — Why the JPY 100,000 and JPY 300,000 lines exist
- Side Note — Why the "Effective Tax Rate" Is Higher Than the Headline Corporate Tax Rate
- Side Note — Why Interim Tax Is Calculated as "Half of Last Year"
- Side Note — Why Is the Consumption Tax Interim Filing Split by "Number of Times"?
- Side Note — Why Does the "Specified Period" Rule Exist as an Afterthought?
- Side Note — How Incorporation Can Stretch the Exemption Period to Nearly 4 Years
- Side Note — Why Would Anyone Choose to Become Taxable?
- Side Note — Why Can't You Just Revert Whenever You Like?
- Side Note — How the T-number borrows from the Corporate Number
- Side Note — Why deemed purchase rates range from 90% down to 40%
- Side Note — Why Is Revoking the Simplified Scheme So Much Simpler?
- Side Note — Why exactly 20%?
- Side Note — Why Did the Deadline Change to "15 Days Before"?
- Side Note — Why the "15 Days Before" Rule Comes Paired With a Transitional Measure
- Side Note — the invoice began life as a packing list
- Side Note — The Origins of the RPM Metric
- Side Note — The Origins of Affiliate Marketing
- Side Note — Why Engagement Rate Matters More Than Follower Count
- Side Note — How Influencer Rates Actually Get Set
- Side Note — Do followers really grow "compounding"?
- Side Note — The "leaky bucket" problem in SaaS
- Side Note — Turning "growth vs. profit" into a single number
- Side Note — the yardstick investors use to size up S&M budgets
- Side Note — Why "how fast you get paid back" shapes company value
- Side Note — A new buzzword born from the end of the zero-interest-rate era
- Side Note — The ideal state of "negative churn"
- Side Note — Why GRR and NRR are usually discussed together
- Side Note — What one canceled account really tells you
- Side Note — Why cohort analysis groups customers by acquisition period
- Side Note — A SaaS metric that measures quality, not just quantity
- Side Note — Why SaaS companies obsess over headcount
- Side Note — Why SaaS companies talk about segments in terms of ARPA
- Side Note — Why the "total amount" alone cannot compare deal sizes
- Side Note — Why sales forecasts multiply in "probability"
- Side Note — Describing sales team productivity with a single number
File Operations
- Side Note — What Can (and Can't) Be Compressed
- Side Note — tar's 512-Byte Blocks and the PAX Extended Header
- Side Note — Why ZIP Filenames Get Garbled
- Side Note — Why Compressing and Bundling Are Separate Tools
- Side Note — Why combine multiple images into one PDF?
- Side Note — What garbled text tells you
- Side Note — why PDFs get so heavy
- Side Note — Why reordering PDF pages has long been such a hassle
Chemistry
- Side Note — Why atomic weights aren't whole numbers
- Side Note — the algorithm behind balancing and the law of conservation of mass
- Side Note — Half-reactions and how batteries work
- Side Note — Where Does the Notation "pH" Come From?
- Side Note — Where the Unit "Molarity" Comes From
- Side Note — De-icers and the chemistry of colligative properties
- Side Note — How the gas laws were unified
- Side Note — When partial pressure becomes a matter of life and death
- Side Note — "Water boils at 100°C" is a conditional fact
- Side Note — A Table Born from Blank Squares and Bold Predictions
- Side Note — Why Radioactive Decay Makes Such a Reliable "Clock"
Physics
- Side Note — Galileo's discovery of the parabola
- Side Note — Galileo's Discovery of the Law of Falling Bodies
- Side Note — When Did the Concept of "Energy" Emerge?
- Side Note — How Coulomb Systematized the Laws of Friction
- Side Note — Where Does the Coefficient of Restitution Come From?
- Side Note — Galileo and the Swinging Lamp
- Side Note — The Newton–Hooke Dispute Over Universal Gravitation
- Side Note — Why a Longer Wrench Makes Loosening Bolts Easier
- Side Note — The Struggle Behind the Discovery of Ohm's Law
- Side Note — The Color Code Follows the Order of the Rainbow
- Side Note — The Puzzle of "More Resistors, Less Resistance"
- Side Note — A Capacitor Code Is the Numeric Cousin of the Resistor Color Code
- Side Note — LC Resonant Circuits and the History of Radio
- Side Note — Why coils borrow the same color language as resistors
- Side Note — How Far the Idea of a Time Constant Reaches
- Side Note — Ever-Shrinking Resistors and Their Marking Tricks
Data
- Side Note — The History and Structure of Japanese Postal Codes
- Side Note — The story behind the National Local Government Code
- Side Note — The History of Bank Codes and Branch Codes
- Side Note — why the last two digits of a country code are called "check digits"
- Side Note — Why the 9th character of a VIN is sometimes "X"
- Side Note — How One Digit Catches a Typo
- Side Note — Why ISBNs Grew From 10 Digits to 13
- Side Note — The mysterious digits under your checkbook
- Side Note — Protected by the same scheme as your credit card
- Side Note — Trivia on country codes and calling codes
- Side Note — Why "Correct" Phone Number Formats Differ So Much Between Countries
- Side Note — Trivia About Airport Codes
- Side Note — Trivia about UN/LOCODEs
Music
- Side Note — Before the Metronome Was Invented
- Side Note — The Hidden History Behind the Number 440Hz
- Side Note — How A=440Hz Became the Standard
- Side Note — Why Musical Intervals Are Measured in Cents, Not a Simple Hz Difference
- Side Note — Why the Circle of Fifths Moves in Fifths
- Side Note — The History of the Capo, a Shortcut for Transposition
- Side Note — How U2's The Edge Popularized the Dotted Eighth Note Delay
- Side Note — Where did the tap tempo button come from?
- Side Note — Why the Same Chord Progression Shows Up in Hundreds of Songs
- Side Note — How Chord Symbols Became a Shared Language
Media
- Side Note — How browsers get access to your camera
- Side Note — Why ID photos dictate the size of your head
- Side Note — What "dBFS" means on a volume meter
- Side Note — "L," "R," and the History of Stereo Sound
- Side Note — Why a single failed pixel is still considered "normal"
- Side Note — how a jamming problem on typewriters gave us the QWERTY layout
- Side Note — A Little History of CPS Testing and Mouse Clicks
- Side Note — Measuring reaction time began with astronomers and their "personal equation"
- Side Note — the history of color vision testing
- Side Note — The "Mosquito Tone" Only Young Ears Can Hear
- Side Note — Why Your Browser Can Record Your Screen at All
Health
- Side Note — Reference values are not a line between "sick" and "healthy"
- Side Note — A formula born in a lab a century ago
- Side Note — Where the "500 kcal rule" came from
- Side Note — Where the Term "Macros" Comes From
- Side Note — why the US Navy built a body fat formula
- Side Note — How measuring body fat has evolved
- Side Note — The History of Measuring Growth With a Single Number
- Side Note — The History of the Widmark Formula and "Calculating Drunkenness"
- Side Note — Where Did 1RM Estimation Formulas Come From?
- Side Note — Why Is a Marathon Exactly 26.2 Miles (42.195 km)?
- Side Note — The History of Naegele's Rule
- Side Note — Where the "28-Day Cycle" Number Comes From
- Side Note — How the "90-Minute Cycle" Was Discovered
Daily Life
- Side Note — The story behind "1 minute on foot = 80 meters"
- Side Note — Why Gas Prices Change Every Week
- Side Note — why the sky is blue and space looks pitch black
- Side Note — Where Does the Phrase "Dog Years" Come From?
- Side Note — Why the Body Condition Score was created
- Side Note — Why energy needs are calculated using "weight to the power of 0.75"
- Side Note — Concrete Has Been Around for Nearly 2,000 Years
- Side Note — Every pebble carries the memory of a place thousands of miles away