significant digits

Significant digits, also called significant figures, are the digits that express a number to a desired accuracy. The significant digits of a given number begin with the first non-zero integer digit or, if this number is less than unity, with the first, zero or non-zero, decimal digit. They end with the final, zero or non-zero, decimal digit; the final zero or zeros of an integer may or may not be significant. For example, 2.871828 to six significant figures is 2.87183 (6 s.f.); to three significant figures it is 2.87 (3 s.f.). See also decimal place.