Accuracy And Precision

NCERT Class 11, Chapter 2 (Units and Measurements) draws a clear distinction between accuracy, which is closeness to the true value, and precision, which is the reproducibility of repeated readings. The student's readings cluster tightly together, indicating high reproducibility and therefore high precision. However, they centre on 48.0 cm rather than the true 50.0 cm, showing a consistent offset and therefore poor accuracy. This is the signature of a systematic error, such as a mis-zeroed instrument. The option accurate but not precise is wrong because the readings are not close to the true value. The option both accurate and precise is wrong as the persistent 2.0 cm deviation rules out accuracy. The option neither accurate nor precise is wrong since the tight clustering demonstrates clear precision. A sanity check confirms that a fixed offset with low scatter is exactly the textbook example of precise but inaccurate measurement.