If a measured quantity is written correctly, which digits are certain? Which are uncertain?
A measured quantity is called significant figures (correct) when it consists of certain and uncertain digits.
Rules for significant figures: A significant figures = certain digit + first uncertain digit
Therefore, the last digit of significant figures are always uncertain.
Let us consider a measured quantity 30.28
Here, (3), (0) and (2) are certain digit and (8) is uncertain digit.