- Significant digits represent ALL measured digits and one estimated digit

- Must assume every number we encounter was measured correctly

- Placeholder zeros are NOT significant digits

• 0.003 ← 1 SF

• 0.00300 ← 3 SF

• 45,000,000 ← 2 SF

• 45,000,000. ← 8 SF

• 4.500 × 10⁷ ← 4 SF

- Scientific notation REMOVES insignificant zeros

• 0.00300 → 3.00 × 10^-3

• 45,000,000 → 4.5 × 10⁷

Math with Significant Digits

- Adding and subtracting: round final answer to the least precise measurement

• 46.1 + 3.995 = 50.095

• tenths =50.1

- Multiplying and dividing: round final answer to the least significant digit

• 46.1 × 3.995 = 184.1695

• 3 4 = 184