In mathematics, the unit of s is seconds. Time unit second is the basic unit of time in the international system of units, with the symbol S, sometimes marked with the English abbreviation sec. The prefix of the international system of units is usually combined with seconds to make a more accurate division. Such as ms (millisecond, thousandth of a second), μs (microsecond, millionth of a second), ns (nanosecond, billionth of a second). Although the international unit prefix system can also be used to extend the time, such as Ks (thousands of seconds), Ms (millions of seconds) and Gs (billions of seconds), it is rarely used in this way, and most people are used to using 60 decimal minutes, hours and 24 decimal days as the extension of seconds.