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Hướng dẫn, bài học và mẹo để tận dụng tối đa các công cụ trực tuyến miễn phí. 120 bài viết.
120 articles — page 4 of 5
William Bengen Built the Retirement Simulation in 1994. His 4% Answer Still Sets the Standard.
A 1994 study of every retirement scenario since 1926 produced the 4% withdrawal rule. Here is what it actually measures and how retirement calculators use it.
A Scanned Image of Your Signature Has the Same Legal Weight as a DocuSign Signature in Most Transactions. Here Is What the Difference Actually Is.
Under the ESIGN Act, a scanned signature and a DocuSign signature are both legally valid. The difference is verifiability and tamper evidence, not legal standing.
Regular Expressions Stopped Being Regular in 1994. Nobody Changed the Name.
Kleene invented regular expressions in 1956 to model neuron firing. Perl made them powerful enough to cause security vulnerabilities. The name never changed.
The Number on the Offer Letter Is Not What You Will Earn. Here Is What You Are Actually Comparing.
A $75,000 salary produces about $55,000 in take-home pay before counting benefits or effective hourly rate. Here's how to compare job offers accurately.
Why Splitting a 200-Page PDF Takes One Second but Splitting a Video Takes an Hour
PDF splits fast because each page is a separate object. Here's how PDF's page tree and cross-reference structure makes splitting lossless, instant, and fundamentally different from editing video.
Your Due Date Comes From a Rule Written in 1806. Here Is Why It Still Works.
Franz Karl Naegele published his 280-day pregnancy rule around 1806. Modern research confirms it still holds for regular cycles. Here is when it breaks down.
Adding 30 Days and Adding One Month Give Different Dates. Here Is Why.
Adding one month to January 31 gives February 28. Adding 30 days gives March 2. Calendar arithmetic is full of edge cases like this. Here is what drives them.
HEIC Is Technically Better Than JPG. Here Is Why You Still Need to Convert.
HEIC stores images at half the size of JPG with better quality. The problem is compatibility. Here is exactly when HEIC works and when converting to JPG is necessary.
A Meter Is Defined by the Speed of Light. An Inch Is Defined by a Meter. The Loop Took 200 Years to Close.
The meter traces back to the speed of light. The inch traces back to the meter. Here is the 200-year story of how two competing measurement systems got entangled.
Benjamin Franklin Left Two Cities Money in 1790. They Got It in 1991.
In 1790 Franklin left 1,000 pounds to Boston and Philadelphia and said wait 200 years. By 1991 it was $20 million each. Here's the math behind how.
41% of Successful Logins Involve a Compromised Password. Here Is How Attackers Use Them.
Cloudflare found that 41% of successful logins involve compromised credentials. Here is how credential stuffing works and how to check without exposing your password.
Fritz Lang Invented the Countdown for a 1929 Film. NASA Used It for Real Rockets.
The rocket launch countdown was invented for dramatic effect in a 1929 silent film. Here is how a filmmaker's device became a universal operational protocol.
Twitter's 140-Character Limit Was Set by SMS Arithmetic in 2006. Here Is What Character Limits Actually Measure.
Twitter chose 140 characters because SMS allows 160 and they needed 20 for a username. Here is what character limits actually measure and why Unicode complicates the count.
There Were 144 Time Zones in North America Before November 18, 1883. Here Is Why Railroads Fixed What Governments Wouldn't.
Before 1883, North America had 144 local time zones. The railroads resolved this in one day without waiting for government action. Here is how it happened.
Email Was Built for Text Only. Base64 Is the 1992 Workaround That Still Runs Email Attachments Today.
Email was designed for 7-bit ASCII text. Base64, invented in 1992 as part of MIME, lets binary files travel through text-only systems. Here is how it works.
A Video File Has Two Tracks. Converting to MP3 Keeps One.
Video files store audio and video as separate independent tracks. Here is how container formats work and why extracting audio keeps 95 percent of the content in 5 percent of the space.
Images Are 60 Percent of the Average Web Page. Here Is Which JPEG Quality Setting You Should Be Using.
Images carry over 60% of a typical web page's byte weight. Here is what JPEG quality settings actually control and what research says about the right setting for web use.
Your Phone Takes JPEGs. Your Accountant Needs PDFs. Here Is the Gap.
Why freelancers and independent contractors convert JPG photos to PDF for tax records, administrative submissions, and document filing workflows.
At 11:59:60 PM, Servers Around the World Panicked. The Single Extra Second That Crashed Reddit in 2012.
On July 1, 2012, a leap second in UTC caused a Linux kernel bug that took down Reddit, Mozilla, LinkedIn, and airline reservation systems for hours.
50% Off Plus 30% Off Is Not 80% Off. Here Is the Math Retailers Count On You Missing.
Sequential percentage discounts compound rather than add. A 50% sale plus a 30% coupon gives 65% off, not 80%. Here's the math behind stacked discounts and anchor pricing.
The Committee That Built an Unkillable Format: JPEG's 36-Year Run
JPEG was designed in 1986 by a committee from IBM, AT&T, and Canon. Here's the math, the patent wars, and why nothing has replaced it in 36 years.
The White Box Problem: What PNG Transparency Becomes in a JPG
Why converting a PNG with transparency to JPG creates a white box, and what to do instead. Covers JPEG's YCbCr model, alpha channels, and format tradeoffs.
She Recorded 18 Podcast Interviews as MP4. She Never Needed the Video.
Recording software captures video even when you only need audio. Here is why converting MP4 to MP3 cuts file size by over 90 percent with no loss to the audience.
URL Shorteners Were Built for Newsgroups. Twitter Nearly Killed Them. Then Twitter Made Them Indispensable.
TinyURL launched in 2002 to fix broken newsgroup URLs. Twitter's 140-character limit in 2009 made shorteners essential. Bitly links hit 2.1 billion clicks in November 2009.