Definitions for "Significant digits"
The number of digits that have been accurately measured. When combining several measurements in a formula, the resulting calculation can only have as many significant digits as the measurement that has the smallest number of significant digits.
a nonzero digit of a decimal numeral whose purpose is more than merely placing the decimal point; (e.g. to express the precision of a measurement to a given level of accuracy – 2.00 kg); example: in 3006, all the digits are significant; in .00498, the zeros are not significant.
the digits required to represent the accuracy of an approximate number, beginning with the leftmost non-zero digit and ending with the rightmost digit
Keywords:  figures, see
see significant figures