Zeros before the first digit are not significant (0.0015 only has 2 Significant Digits)
Zeros between other digits are significant (1005 has 4 significant digits)
Zeros after other digits following a decimal place are significant (5.30 has 3 Significant Digits)
Zeros at the end of a number are significant only if indicated by scientific notation
4.1 * 10 has 2 Significant Digits
4.10 * 10 has 3 Significant Digits
4.100 * 10 has 4 Significant Digits
4.01 * 10 has 2 significant digits