<P> A limited number of countries, particularly English - speaking nations, use the 12 - hour clock as a standard, or a mixture of the 24 - and 12 - hour time systems . In countries where the 12 - hour clock is still 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 . In the United States and a handful of other countries, it is popularly referred to as military time . </P> <P> 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, but it is optional for the hours . The leading zero is very commonly used in computer applications, and always used when a specifications require it (for example, ISO 8601). </P> <P> 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". </P> <P> In East Asia, time notation was 24 - hour before westernization in modern times . Western - made clocks were changed into 12 dual - hours style when they were shipped to China in the Qing dynasty . </P>

What is 1 day and 9 hours from now