|
The 24-hour clock is the convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, indicated by the hours passed since midnight, from 0 to 23. This system is the most commonly used time notation in the world today,〔See the Common Locale Data Repository for detailed data about the preferred date and time notations used across the world, as well the locale settings of major computer operating systems, and the article Date and time notation by country.〕 and is used by international standard ISO 8601.〔International Standard ISO 8601: Data elements and interchange formats – Information interchange – Representation of dates and times. International Organization for Standardization, 3rd ed., 2004.〕 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.〔Gloria D. Pickar (2011), Dosage Calculations, Cengage Learning, 537 pp. (p.60)()〕 It is popularly referred to as military time in the United States, English-speaking Canada,〔U.S. Government Printing Office, Style Manual. 〕 and a handful of other countries〔 where the 12-hour clock is still dominant. ==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. In the case of a leap second, the value of ss may extend to 60. A leading zero is added for numbers under 10. This zero is optional for the hours, but very commonly used in computer applications, where many specifications require it (for example, ISO 8601). Where subsecond resolution is required, the seconds can be a decimal fraction, that is, the fractional part follows a decimal dot or comma, as in 01:23:45.678. The most commonly used separator symbol between hours, minutes and seconds is the colon, which is also the symbol used in ISO 8601. In the past, some European countries used the dot on the line as a separator, but most national standards on time notation have since then been changed to the international standard colon. In some contexts (including the U.S. military and some computer protocols), no separator is used and times are written as, for example, "2359". ===Midnight 00:00 and 24:00=== In the 24-hour time notation, the day begins at midnight, 00:00, and the last minute of the day begins at 23:59. Where convenient, the notation 24:00 may also be used to refer to midnight at the end of a given date〔ISO 8601:2004 ''Data elements and interchange formats – Information interchange – Representation of dates and times'', clause 4.2.3 Midnight〕that is, 24:00 of one day is the same time as 00:00 of the following day. The notation 24:00 mainly serves to refer to the exact end of a day in a time interval. A typical usage is giving opening hours ending at midnight (e.g. "00:00–24:00", "07:00–24:00"). Similarly, some railway timetables show 00:00 as departure time and 24:00 as arrival time. Legal contracts often run from the start date at 00:00 until the end date at 24:00. While the 24-hour notation unambiguously distinguishes between midnight at the start (00:00) and end (24:00) of any given date, there is no commonly accepted distinction among users of the 12-hour notation. Style guides and military communication regulations in some English-speaking countries discourage the use of 24:00 even in the 24-hour notation, and recommend reporting times near midnight as 23:59 or 00:01 instead.〔"(Communication instructions – General )", Allied Communications Publication ACP 121(I), page 3–6, Combined Communications-Electronics Board, October 2010〕 Sometimes the use of 00:00 is also avoided.〔 In variance with this, the correspondence manual for the U.S. Navy and U.S. Marine Corps formerly specified 0001 to 2400.〔SECNAV M-5216.5 Department of the Navy Correspondence Manual dated March 2010, Chapter 2, Section 5 Paragraph 15. Expressing Military Time.〕 The manual was updated in June 2015 to use 0000 to 2359. 〔http://www.marines.mil/Portals/59/Publications/SECNAV%20M%205216.5.pdf〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「24-hour clock」の詳細全文を読む スポンサード リンク
|