Counting significant figures:

1. All non-zero digits are significant: 345 has 3 SF
2. Zeros between non-zero digits are significant: 3005 has 4 SF
3. Leading zeros are NOT significant: 0.0034 has 2 SF
4. Trailing zeros after decimal point ARE significant: 3.400 has 4 SF
5. Trailing zeros in whole number without decimal point are ambiguous: 2300 could be 2, 3, or 4 SF (use scientific notation to clarify)

Arithmetic rules:

• Multiplication/Division: result has fewest SF of the inputs
• Addition/Subtraction: result has fewest decimal places of the inputs
• Exact numbers (counting, defined values) have infinite SF

Example: 3.24 * 2.1 = 6.804 -> 6.8 (2 SF, limited by 2.1) Example: 3.24 + 2.1 = 5.34 -> 5.3 (1 decimal place, limited by 2.1)