Dating is Hard: Complexity of Clocks, Calendars, and Computers

A presentation at WebExpo Prague 2025 in May 2025 in Prague, Czechia by Robin Pokorny

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Robin Pokorny 2025-05-28 Complexity of Clocks, Calendars, and Computers

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2 Intro WHAT IS THE ?

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Intro 3 The twenty-eighth of May, two thousand and twenty-five at two o’clock in the afternoon

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History 4 HUMAN-MADE

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5 History GOLDEN RATIO?

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6 Example 28 May 2025, 2 pm

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Example 2025-05-28T14:00:00 7

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Example 2025-05-28T14:00:00 8

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9 Example 20250528T140000

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Example 2025-W22-3T14:00:00 10

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11 Example 2025W223T140000

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12 Example 2025-148T14:00:00 2025148T140000

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Unix time: seconds or milliseconds? 1748433600000 1748433600 14

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15 Solution for computers WHAT TO DO USE RFC 3339 DO NOT USE ISO

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Example 16 2025-05-28T14:00:00+02:00 2025-05-28T12:00:00Z

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Compare 17 Source

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18 Solution for computers WHAT TO DO USE RFC 9557 Internet Extended Date/Time Format (IXDTF) USE RFC 3339 DO NOT USE ISO

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Example 19 2025-05-28T14:00:00+02:00[Europe/Prague] 2025-05-28T12:00:00Z[Europe/Prague]

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20 Example 2025-01-28T14:00:00+02:00[Europe/Prague] Inconsistent

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21 Example 2035-05-28T13:00:00+01:00[Europe/Prague] Inconsistent

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22 Temporal API Temporal API Upcoming replacement for the Date object with full RFC 9557 (IXDTF) support and time zone arithmetic.

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Temporal API 23 Gist

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24 Cheat sheet Storage and transport Y Instant? Y Past? N RFC 3339/9557 with Z Unix timestamp RFC 9557 (Local/Z + zone) N RFC 9557 (Local + zone) by robinpokorny.com

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Solution for people Wednesday, 28 May 2025, 2 pm (Prague) Wed, 28 May, 2 pm PRG 25

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Thanks THINK ABOUT YOUR DATES! me@robinpokorny.com 26

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