Distinguish Between Accuracy and Precision

• Definition: Accuracy refers to how close a measured value is to the actual (true) value.
• Meaning: If a textbook weighs exactly 2.0 kg, and your weighing scale says 2.01 kg, your scale is highly accurate. If it says 3.5 kg, it is inaccurate.
• Depends on: Calibration of the instrument. Systematic errors reduce accuracy.

• Definition: Precision refers to how close multiple measurements are to each other, regardless of whether they are close to the true value.
• Meaning: It describes the exactness or resolution of the instrument. A scale that measures up to 3 decimal places (2.015 kg) is more precise than one measuring 1 decimal place (2.0 kg).
• Depends on: The least count of the instrument. Random errors reduce precision.

Imagine throwing darts at a dartboard (the bullseye is the 'true value'):

1. Accurate & Precise: All darts hit right in the bullseye.
2. Precise but NOT Accurate: All darts hit closely together, but far away from the bullseye (e.g., in the top right corner).
3. Accurate but NOT Precise: Darts are scattered widely around the board, but their average centre is the bullseye.
4. Neither: Darts are scattered widely and far from the bullseye.