Key Concepts: Accuracy, Precision, & Significant Figures

Accuracy vs Precision

• Accuracy: How close a measurement is to the true (accepted) value. High accuracy = small systematic error.
• Precision: How close repeated measurements are to each other. High precision = small random error.
• A measurement can be precise but not accurate (consistently wrong), or accurate but not precise (scattered around the true value).

Significant Figures

• All nonzero digits are significant: 123 has 3 sig figs.
• Zeros between nonzero digits are significant: 1002 has 4 sig figs.
• Leading zeros are NOT significant: 0.0045 has 2 sig figs.
• Trailing zeros after a decimal point ARE significant: 2.50 has 3 sig figs.

Rules for Calculations

• Multiplication/Division: Result has the same number of sig figs as the factor with the fewest.
• Addition/Subtraction: Result is rounded to the same decimal place as the least precise input.