If someone in Alberta discussed a meeting with someone in Britain "let's say 12:00 London time" and the Albertan recorded that as 05:00 in their own calendar, then how can the software know that this should now be 06:00?

The Albertan could have set the time to 12:00 in Europe/London, but probably few people do this unless they're expecting to travel to the other place.

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tetraodonpuffer 9 hours ago | parent | next [-]

it seems an unsolvable problem either way, the meeting is "at 12:00 london"

1. the London person owns it, schedules in local (London) time 12:00

2. the London person owns it, schedules mental math explicit Alberta time 05:00

3. the Alberta person owns it, schedules in local (Alberta) mental math time 05:00

4. the Alberta person owns it, schedules in explicit London time 12:00

You cannot get all of these working by software only no matter what you do, because there "mental math" time cannot take into account the implicit expectations, 1 and 4 will be correct as stated (the meeting is at 12 London time) but 2 and 3 what do you do? How would you differentiate between "mental math what I thought Alberta time was" vs "I really meant it at this Alberta time"

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mrpotato 8 hours ago | parent | prev [-]

The problem you are describing is solved by saving/persisting times in UTC. The calendar will display the event by using the user's current timezone and the UTC time to determine local time.

	▲	rjrjrjrj 7 hours ago \| parent \| next [-]
		You can store times in UTC if you want, but that alone doesn't solve the problem. A UTC timestamp alone is not enough information about an event. Consider a Doctor's appointment for Dec 20, 2026 2pm in Calgary. Regardless of whether its booked a year ahead (ie before the new time zone rules were decided) or a week ahead (after the rules were decided, and consequently a different UTC time), the expectation is that it will be at at 2pm local time.
	▲	jessekv 7 hours ago \| parent \| prev \| next [-]
		Generally speaking, UTC + localization works for past events, but not future ones (see sibling comments)
	▲	Symbiote 8 hours ago \| parent \| prev [-]
		But doing that breaks the opposite (and more common) problem: all the meetings in Alberta, planned before the change to the time zone was announced, will have the wrong hour.