Measurement
Accuracy & precision
Same target every shot? Or close to bullseye? They're different things.
Accuracy is how close you are to the true value. Precision is how consistently you get the same value. They're not the same thing.
Try this
49.5
how accurate is this reading? = Off by 0.5 (1.0% error) — fairly accurate
Accuracy vs precision
- Accuracy — how close you are to the true value.
- Precision — how close repeated readings are to *each other*.
- Accurate + precise: bullseye every time.
- Precise but not accurate: tight cluster, wrong spot.
A bathroom scale that always reads 2 kg high is precise (same answer every time) but inaccurate. A scale that jumps around ±2 kg but averages right is the opposite.
Your turn
Three readings of a 10.0 g mass: 12.1, 12.0, 12.2 g. Accurate, precise, both, or neither?
Bullseye every time = accurate AND precise. Tight cluster off-target = precise but inaccurate. Scattered around bullseye = accurate but imprecise. Scattered all over = neither.