What happens when a phone scans an event code
The code holds a short calendar record in iCalendar format, starting BEGIN:VCALENDAR. A phone that recognises it shows the event and offers to add it to a calendar. The iPhone Camera app is one that recognises calendar events, and some Android scanners offer the same.
What happens next depends on the phone and its calendar app. Some show the description and the link, and some show only the title, time and place. Some scanner apps show the raw text instead of a calendar entry. Scan the code on the phones your guests are likely to have, and print the date, time and place in words as well, in case a scan does not work.
The person chooses whether to add the event, so nothing lands in a calendar without them agreeing.
Time zones: same clock time, UTC or a named zone
The time zone setting decides how the start and the end are written into the code:
- Same clock time everywhere (also called floating time): the code says 19:00 with no zone, and every phone shows 19:00 on its own clock. This is right for a local event, such as a school fair or a shop opening, where everyone is in the same place. It is wrong for an event that people in different zones attend.
- A named time zone, such as Europe/Paris: the tool takes 19:00 in Paris, works out the exact moment using that zone's rules for that date, daylight saving time included, and stores it in UTC. A phone in another zone then shows the correct local time for that date, for example 13:00 on a phone in New York in summer.
- UTC: for events scheduled by universal time, such as an online broadcast. The code stores your time as UTC.
The code stores the moment in UTC rather than the zone's name, because a zone name only works reliably when the zone's rules travel with it, which would make the code much bigger. Because of this, a phone shows the event in its own zone, not in the zone you picked. Print the local time on the poster too, so that nobody is surprised.
When the clocks go back, one hour happens twice, and the tool uses the first. When the clocks go forward, a time inside the skipped hour is moved to after the change.
All day and multi day events
Turn on All day and the start and end become dates. Choose the first and last day: a conference from 12 to 14 October takes the 12th as the first day and the 14th as the last. The tool writes the end as the day after the last day, because that is how the format counts, and calendar apps show it as covering the three days.
An all day event has no clock time and no time zone, so it lands on the same date for everyone who scans it.
What to put in it, and what it costs in squares
Every character in the event takes space in the code. At medium error correction these are typical sizes:
- Title with start and end times: 57 by 57 squares
- The same with a location and a short description: 65 by 65
- An all day event with a title of up to 12 characters: 57 by 57. With the title Studio open day it is 61 by 61
The format has fixed parts that always take some room, so even a short event is bigger than a link or a contact. For a poster, print the code at least 3 cm wide, and bigger if people will scan it from a distance. If you have a lot to say, put it on a web page and add its address in the Link box.
Without an end time the tool warns you, because calendar apps then show the event with no length. Repeating events, reminders and guests are not part of this tool, and a printed code cannot be updated, so if the date changes you make a new code and replace the old one.