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Luckily, Google Calendar takes care of this problem quite nicely:
- Go to Settings -> General -> Your current time zone
- Set your primary time zone if you haven't done so yet
- Check "Display all time zones" for full list of time zones
- Click on the "Show an additional time zone" link to add another time zone
- Chose you additional time zone from the list
- Enter your custom labels
- Save changes, and your appointments will have a nice label for each time zone next to them: