Daylight Savings Editor

This is a Daylight Savings Editor for Mac OS 8.5 to 9.2.2. It edits the 'loc#' resource in the System file which contains all the time zone parameters for various cities around the world. You will need to restart your computer after making changes for those changes to take effect. Make sure the Date & Time control panel is not open when running this.

You use this at your own risk, I accept no responsibility if this application causes any problems. It is a good idea to save a copy of your System file, the Date & Time control panel, and the Date & Time Preferences before making any changes.

Version 1.0a1 does not support internationalized systems where the name of the Date & Time control panel and the Date & Time Preferences are different.

Version 1.0a1 only supports changing the daylight savings parameters for existing cities. It does not yet support adding cities.

Version 1.0d2 fixed a bug where changing the None/Manual/Automatic setting would result in a corrupted city list until it was changed back. It also synchronizes the settings between the System file, the Date & Time control panel, and the Date & Time Preferences.

Version 1.0d3 adds support for editing the UTC offset of the city.

Version 1.0a1 has a new feature where you can choose to install a new time zone set created from tzdata 2023c. Just go to the file menu and choose the install option. The original Mac OS 9 time zones can also be installed from the File menu.

As well as updating all the time zones with current UTC offsets and daylight savings information, the following changes are also included in the tzdata 2023c set:
Renamed the country Turkey to Türkiye
Renamed the following cities:
Dacca to Dhaka
Katmandu to Kathmandu
Calcutta to Kolkata
Kiev to Kyiv
Ndjamena to N'Djamena
Port-Au-Prince to Port-au-Prince
St. Petersburg to Saint Petersburg
Washington to Washington, D.C.
Rangoon to Yangon

Other changes in 1.0a1 include:
Fixed a bug where changes that make the loc# resource larger could fail.
Cities can also be removed.
It is now possible to specify daylight savings rules for a day of the week on or after a specific day of the month (e.g.: Asunción, Jerusalem, Santiago)

Click here to download Daylight Savings Editor 1.0a1 (StuffIt archive - 19k)

The format of the 'loc#' resource is a revision of the 'CTY#' resource in earlier systems. The format of 'CTY#' resources is somewhat documented here. The first 12 bytes within a city entry, the latitude/longitude/GMT difference, is actually a MachineLocation struct.

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