The most significant figure in a number is the first non-zero
digit starting from the left. In the number 238.95, for example,
although the left-hand digit is only 2 it represents 200,
while the largest digit 9 only represents 9 tenths. The next
most significant digit is the 3 for it represents 30, while
the least significant digit is the 5 as it only represents
5 hundredth. Numerical calculations are often rounded off
to a specified number of significant figures, shortened to
sig. Fig. Or s.f. The examples below show the result of various
calculations, and the effect of rounding them to the number
of significant figures stated:

9.434 285 to 4 Significant Figures is 9.434

546.3287 to 3 Significant Figures is 546

0.490 12 to 3 Significant Figures is 0.490

0.002 054 to 2 Significant Figures is 0.0021.