Significant digits In multiplication or division, the number with the fewest significant digits determines the number of significant digits in the answer (2.7 x 28.8765 x 0.00374283300164 = 0.29). In addition or subtraction, the largest number determines the number of significant digits (1234 + 1.2 = 1235). In a measurement, the error determines the number of significant digits (271.4165 ± 0.1 m = 271.4 m). The zero before the decimal point is not a significant digit (0.29 has two significant digits); zeros at the end of a number are significant (250 000 000 and 250.000 000 have nine significant digits). If the former should have only three, write it as 2.50 x 108. In some cases, this may be avoided by the use of appropriate units (2.50 x 108 a = 0.250 Ga = 250 Ma). See Units of measure.