{"templateId":"markdown","sharedDataIds":{"sidebar":"sidebar-sidebars.yaml"},"props":{"metadata":{"markdoc":{"tagList":["admonition"]},"type":"markdown"},"seo":{"title":"Timezone Offset ( timezoneOffset )","llmstxt":{"hide":true}},"dynamicMarkdocComponents":[],"compilationErrors":[],"ast":{"$$mdtype":"Tag","name":"article","attributes":{},"children":[{"$$mdtype":"Tag","name":"Heading","attributes":{"level":1,"id":"timezone-offset--timezoneoffset-","__idx":0},"children":["Timezone Offset (",{"$$mdtype":"Tag","name":"code","attributes":{},"children":["timezoneOffset"]},")"]},{"$$mdtype":"Tag","name":"Heading","attributes":{"level":2,"id":"overview","__idx":1},"children":["Overview"]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["A ",{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/glossary#timezone-offset"},"children":["timezone offset"]}," is a positive or negative integer representing an offset from ",{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/glossary#utc"},"children":["UTC"]}," in minutes. For example, San Francisco is –480 minutes (eight hours) behind UTC, reflecting that you must ",{"$$mdtype":"Tag","name":"em","attributes":{},"children":["subtract"]}," eight hours from UTC to get ",{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"https://www.timeanddate.com/worldclock/difference.html?p1=3875"},"children":["the local time"]},"."]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["Date & time settings changes in a device’s history will factor into updates to the stored timezone offset, conversion offset, or clock drift offset."]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["The original version of BtUTC only stored a timezone offset because it was primarily concerned with solving the two most common-use cases for device time changes on diabetes devices:"]},{"$$mdtype":"Tag","name":"ul","attributes":{},"children":[{"$$mdtype":"Tag","name":"li","attributes":{},"children":["Changes resulting from the shift to or from ",{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/glossary#dst"},"children":["DST"]}]},{"$$mdtype":"Tag","name":"li","attributes":{},"children":["Changes resulting from travel across timezones"]}]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["These changes are interpreted as changes to the stored timezone offset on each datum."]},{"$$mdtype":"Tag","name":"hr","attributes":{},"children":[]},{"$$mdtype":"Tag","name":"Heading","attributes":{"level":2,"id":"time-field-relationships","__idx":2},"children":["Time Field Relationships"]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["Overall, the relationship between the following fields in the Tidepool data model — device time, time, timezone offset, conversion offset and clock drift offset — can be generalized as follows (assuming all appropriate unit conversions have been made):"]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":[{"$$mdtype":"Tag","name":"code","attributes":{},"children":["Device time = time + timezone offset + conversion offset"]}]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["In the most current (and production) version of BtUTC, clock drift offset is stored for data auditing and provenance only."]},{"$$mdtype":"Tag","name":"hr","attributes":{},"children":[]},{"$$mdtype":"Tag","name":"Heading","attributes":{"level":2,"id":"finding-a-timezone-offset","__idx":3},"children":["Finding A Timezone Offset"]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["If you do not have the timezone offset for a particular datum and want to find it, you need two pieces of information:"]},{"$$mdtype":"Tag","name":"ol","attributes":{},"children":[{"$$mdtype":"Tag","name":"li","attributes":{},"children":["The local timezone name"]},{"$$mdtype":"Tag","name":"li","attributes":{},"children":["The local datetime OR the UTC time"]}]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["Because timezones do not always map directly to timezone offsets, another anchor is needed to decide which offset associated with a named timezone to map to. Either the local datetime or the true UTC time for the datum can serve as this anchor."]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["The reverse is also true: Timezone offsets do not map directly to timezones. For example, Arizona does not participate in ",{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/glossary#utc"},"children":["DST"]}," and has a timezone offset of –420 minutes to UTC year-round. Whereas neighboring New Mexico shares the same offset when DST is ",{"$$mdtype":"Tag","name":"em","attributes":{},"children":["not"]}," in effect, but has an offset of –360 minutes to UTC when DST ",{"$$mdtype":"Tag","name":"em","attributes":{},"children":["is"]}," in effect."]},{"$$mdtype":"Tag","name":"hr","attributes":{},"children":[]},{"$$mdtype":"Tag","name":"Heading","attributes":{"level":2,"id":"upper-threshold-for-timezone-offset-changes","__idx":4},"children":["Upper Threshold For Timezone Offset Changes"]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["In occasional instances, a user sets the time on the diabetes device to the wrong month or year and must later correct it. We do not interpret such massive changes to the date & time settings as an adjustment to the timezone offset. Rather, whenever a date & time settings change is larger than the maximum difference possible by traveling between timezones (1,560 minutes), we apply this change as an adjustment to the ",{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/btutc/conversion"},"children":["conversion offset"]},"."]},{"$$mdtype":"Tag","name":"hr","attributes":{},"children":[]},{"$$mdtype":"Tag","name":"Heading","attributes":{"level":2,"id":"timezone-offset-abbreviations","__idx":5},"children":["Timezone Offset Abbreviations"]},{"$$mdtype":"Tag","name":"p","attributes":{},"children":["There is a set of three-letter and four-letter codes used to abbreviate timezone and timezone offset information. For example, PST (Pacific Standard Time) refers to the US/Pacific timezone, which has an offset of –480 minutes to UTC. PDT (Pacific Daylight Time) refers to the same timezone when ",{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/glossary#dst"},"children":["DST"]}," is in effect."]},{"$$mdtype":"Tag","name":"Admonition","attributes":{"type":"info"},"children":[{"$$mdtype":"Tag","name":"p","attributes":{},"children":["It is important to keep these abbreviations distinct from timezone names. Do not use an abbreviation where a timezone is requested, and vice versa."]}]},{"$$mdtype":"Tag","name":"hr","attributes":{},"children":[]},{"$$mdtype":"Tag","name":"Heading","attributes":{"level":2,"id":"keep-reading","__idx":6},"children":["Keep Reading"]},{"$$mdtype":"Tag","name":"ul","attributes":{},"children":[{"$$mdtype":"Tag","name":"li","attributes":{},"children":[{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/btutc"},"children":["Bootstrapping to UTC"]}]},{"$$mdtype":"Tag","name":"li","attributes":{},"children":[{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/btutc/usage"},"children":["BtUTC Usage"]}]},{"$$mdtype":"Tag","name":"li","attributes":{},"children":[{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/btutc/clock-drift"},"children":["Clock Drift Offset"]}]},{"$$mdtype":"Tag","name":"li","attributes":{},"children":[{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/btutc/conversion"},"children":["Conversion Offset"]}]},{"$$mdtype":"Tag","name":"li","attributes":{},"children":[{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/glossary"},"children":["Datetime Glossary"]}]},{"$$mdtype":"Tag","name":"li","attributes":{},"children":[{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime"},"children":["Datetime Guide"]}]},{"$$mdtype":"Tag","name":"li","attributes":{},"children":[{"$$mdtype":"Tag","name":"MarkdownLink","attributes":{"href":"/docs/datetime/assumptions"},"children":["Incorrect Assumptions about Datetime"]}]}]}]},"headings":[{"value":"Timezone Offset ( timezoneOffset )","id":"timezone-offset--timezoneoffset-","depth":1},{"value":"Overview","id":"overview","depth":2},{"value":"Time Field Relationships","id":"time-field-relationships","depth":2},{"value":"Finding A Timezone Offset","id":"finding-a-timezone-offset","depth":2},{"value":"Upper Threshold For Timezone Offset Changes","id":"upper-threshold-for-timezone-offset-changes","depth":2},{"value":"Timezone Offset Abbreviations","id":"timezone-offset-abbreviations","depth":2},{"value":"Keep Reading","id":"keep-reading","depth":2}],"frontmatter":{"seo":{"title":"Timezone Offset ( timezoneOffset )"}},"lastModified":"2025-09-04T14:19:18.000Z","pagePropGetterError":{"message":"","name":""}},"slug":"/docs/datetime/btutc/timezone","userData":{"isAuthenticated":false,"teams":["anonymous"]},"isPublic":true}