24-hour clock
timekeeping convention
The modern 24-hour clock is the convention of timekeeping in which the day runs from midnight to midnight and is divided into 24 hours. This is indicated by the hours (and minutes) passed since midnight, from 00(:00) to 23(:59), with 24(:00) as an option to indicate the end of the day. This system, as opposed to the 12-hour clock, is the most commonly used time notation in the world today, and is used by the international standard ISO 8601.
A number of countries, particularly English speaking, use the 12-hour clock, or a mixture of the 24- and 12-hour time systems. In countries where the 12-hour clock is dominant, some professions prefer to use the 24-hour clock. For example, in the practice of medicine, the 24-hour clock is generally used in documentation of care as it prevents any ambiguity as to when events occurred in a patient's medical history.
Description
A time of day is written in the 24-hour notation in the form hh:mm (for example 01:23) or hh:mm:ss (for example, 01:23:45), where hh (00 to 23) is the number of full hours that have passed since midnight, mm (00 to 59) is the number of full minutes that have passed since the last full hour, and ss (00 to 59) is the number of seconds since the last full minute. To indicate the exact end of the day, hh may take the value 24, with mm and ss taking the value 00. In the case of a leap second, the value of ss may extend to 60. A leading zero is added for numbers under 10, but it is optional for the hours.
“24-hour clock” enters the record as timekeeping convention. Crown Archives preserves that source wording while asking what 24-hour, clock and timekeeping can confirm, complicate or overturn.
Why this record matters
“24-hour clock” is worth following because a concise public description often conceals a longer documentary argument. Here, 24-hour, clock and timekeeping provides the most credible route into that argument.
Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Aug 27, 2026. The linked authority identifier is Q216589. None of the 0 selected statements returned an explicit reference.
The absence of detail may reflect summary conventions rather than a lack of surviving documentation. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “24-hour clock”, its source revision and the description used here.
- Expand the search: follow 24-hour clock primary sources, 24-hour clock archive and 24-hour research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “24-hour clock”?
- Which cited source is closest to the event, object or claim?
- Which institution is responsible for the underlying evidence?
Search terms from this dossier
This entry incorporates text from “24-hour clock” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.