- Practice · 3+3 marks
Accuracy, precision, sensitivity, resolution
Short answer
Accuracy is closeness to true value; precision is repeatability. Example: clustered shots far from bullseye are precise but inaccurate. Sensitivity = Δoutput/Δinput; threshold is smallest input from zero that yields output; resolution is smallest detectable change from any value; tolerance is maximum permitted error from a specified value.
(a) Differentiate between accuracy and precision with a suitable example.
(b) Define sensitivity, threshold, resolution and tolerance of a measuring instrument.
(a) Accuracy and precision
Accuracy is the closeness of a measured value to the true value. Precision is the closeness of repeated readings of the same quantity to each other (repeatability).
| Point | Accuracy | Precision |
|---|---|---|
| Meaning | Nearness to true value | Nearness of readings to one another |
| Error type | Affected by systematic error | Affected by random error |
| Expressed as | % of full scale or % of reading | Standard deviation, repeatability |
| Improved by | Calibration | Better design, averaging |
| Possible alone? | Average of scattered readings can be accurate | Readings can be precise yet wrong |
Example: a target shot. Shots all clustered far from the bullseye are precise but not accurate. Shots scattered evenly around the bullseye are accurate on average but not precise. A voltmeter reading 4.98, 4.99, 4.98 V for a true 5.50 V is precise but inaccurate.
(b) Definitions
- Sensitivity: ratio of the change in output to the change in input, (slope of the calibration curve). Example: 5 mV/bar.
- Threshold: the smallest input change from zero that produces a detectable output.
- Resolution: the smallest change in input (from a non-zero value) that the instrument can detect. For a digital meter it is one least-count digit.
- Tolerance: the maximum permitted departure from a specified value, usually given as value or ; it is the permissible error, not the instrument's inherent accuracy.
✓ Answer checked by Claude Opus 5.5 (high effort)
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