• All non-zero digits in a number are significant.
Example: Numbers 0.0000216, 0.0216, 21.6 and 216 have the same
number of significant figures namely three (2, 1, 6).
• All zeros between two non-zero digits are significant, no matter where the decimal point is, if at all.
Example : In the numbers 0.0000206, 0.0206, 20.6 and 206, the zero lying between the digits 2 and 6 is only significant.
• If the number is less than 1, the zeroes on the right of decimal point but to the left of the first non-zero digit are not significant.
Example : In 0.0000206, the four zeros after decimal and before the digit 2 has no significance. Similarly, in 0.0206, the zero after decimal and before the digit 2 has no significance. So the number of significant figures of these numbers are three (2, 0 and 6).
• The terminal or trailing zeros in a number without a decimal point are significant depending on accuracy of measurement.
Example : In 2360 m, the terminal zero has no significance, if the accuracy of measurement is 10 m then the number of significant figures of this number is three (2, 3 and 6). If the accuracy of measurement is 1 m, the terminal zero is significant figures of this same number will be four (i.e. 2, 3, 6 & 0).
• The digit 0 conventionally put on the left of a decimal for a number less than 1 is never significant. However, the zeros at the end of such number are significant in a measurement.
Example : The number 0.120 has three significant numbers. The zero before the decimal point is not significant.
• The terminal or trailing zeros in a number with a decimal point are significant.
Example : In 23.60 m, the terminal zero has significance, so the number of significant figures in this number is four (2, 3, 6 and 0).