how do you tell how many significant digits are included in a number
There are four rules in determining significant figures on numbers with a decimal point.
1. All non-zero digits are significant. (12345.54 has 7 significant figures)
2. Leading zeros are not significant (0.00000000000000000004 has only 1 significant figure)
3. Trailing zeros are significant. (54.49000 has 7 significant figures)
4. Zeros between significant figures are also significant. (40.0040 has 6 significant figures)
Whole numbers have ambiguous number of significant figures. 695000 can have 6, 5, 4,or only 3.