Time unit is one of the seven basic units. Length, time, mass, quantity of matter, illumination, current and (thermodynamic) temperature are seven basic units.
1, year: the unit of time in which events related to the earth's revolution around the sun occur repeatedly. In the modern Gregorian calendar, the average year is 365 days (including 52 weeks 1 day), and the leap year is 366 days (including 52 weeks and 2 days). English means year and is often used as y.
2. Month: the time unit in the calendar, and a year is divided into 12 months; In China, the lunar year is 12 months and the leap year is 13 months. The extra month is called leap month. English means month, often m.
3. Day: The day is the time unit to measure the rotation of the planet. English means day, usually D.
4. Hour: The hour is not the basic unit of the international system of time units (the basic unit of the international system of time units is seconds), but an auxiliary unit of time coordinated with the basic unit of the international system of units.
Except leap second, one hour is generally equal to 3600 seconds, or 60 minutes, or 1/24 days. "H" is often used in English class or math.
5. Minute: the unit of measurement of time. Minute is English, which means "tiny" and also means min.
6. seconds: the basic unit of time in the international system of units, with the symbol S. Sometimes it is marked as seconds with English abbreviations.
The prefix of the international system of units is often combined with seconds to make a finer division, such as ms (millisecond, thousandth of a second), μs (microsecond, millionth of a second) and ns (nanosecond, billionth of a second).