All non-zero digits are significant: 1, 2, 3, 4, 5, 6, 7, 8, 9.
Zeros between non-zero digits are significant: 102, 2005, 50009.
Leading zeros are never significant: 0.02, 001.887, 0.000515.
In a number with a decimal point, trailing zeros (those to the right of the last non-zero digit) are significant: 2.02000, 5.400, 57.5400.
In a number without a decimal point, trailing zeros may or may not be significant. More information through additional graphical symbols or explicit information on errors is needed to clarify the significance of trailing zeros.