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localdatetime.now guides & articles

10 in-depth guides on Local Date & Time and related topics.

Reference

Reference Date Formats Around the World: Who Writes What, and Why A reference to the three ways the world orders day, month and year, which countries use each, why 03/04 is genuinely ambiguous, and what to write instead. 6 min read Reference ISO Week Numbers: The First Thursday Rule Explained The rules behind ISO week numbering: weeks start on Monday, week 1 holds the first Thursday of January, and the consequences that follow at every year boundary. 5 min read Reference RFC 2822 vs ISO 8601: Two Timestamp Formats and When to Use Each A side-by-side reference on the RFC 2822 email date format and ISO 8601, covering where each is required, how RFC 3339 fits in, and which one to write. 5 min read Reference What Is My UTC Offset? How Offsets Work and How to Read Them A reference on UTC offsets: what the signed number actually measures, how it differs from a time zone, why it shifts with daylight saving, and how browsers work it out. 5 min read

Concepts explained

Concepts explained Browser Local Time: How Browsers Determine the Time You See Where a web page gets the time it shows you: the operating system clock, the configured zone, the IANA database, and the JavaScript APIs that read them. 5 min read Concepts explained ISO 8601 Explained: The Date Format That Ends Ambiguity How the ISO 8601 date and time standard is built: field ordering, the T separator, Z and numeric offsets, durations and intervals, and why the format sorts correctly as plain text. 6 min read Concepts explained Leap Seconds Explained: Why Clocks Occasionally Gain a Second Why an extra second is occasionally inserted into Coordinated Universal Time, who decides, how computers cope with a minute of 61 seconds, and why the practice is ending. 5 min read Concepts explained The Year 2038 Problem: When 32-Bit Time Runs Out Why 32-bit systems stop being able to tell the time at 03:14:07 UTC on 19 January 2038, which parts of the stack are already fixed, and which are not. 5 min read Concepts explained Unix Epoch Time Explained: Seconds Since 1970 What a Unix timestamp actually counts, why the origin is 1 January 1970, how to tell seconds from milliseconds, and why the number carries no time zone of its own. 6 min read Concepts explained Why You Should Store Dates in UTC (and When You Should Not) The case for keeping every recorded instant in UTC, the two daylight saving failures that destroy local timestamps, and the one situation where UTC alone is not enough. 6 min read