Q.Define precision and accuracy. Explain with one example.

Two terms that are used loosely in everyday speech mean two genuinely different things in measurement science:

• Accuracy -- how close a measured value is to the true (theoretical) value.
• Precision -- how close repeated readings are to one another, i.e. how reproducible the measurement is -- regardless of whether that cluster of readings is anywhere near the truth.

Worked example (temperature). If a refrigerator's real temperature is $9^\circ$C, and a thermometer repeatedly reads $10.4,10.2,10.3,10.1,10.2,10.1,10.1,10.1$ ($^\circ$C), the readings cluster tightly around $10^\circ$C -- the thermometer is precise -- but since $10^\circ$C is about $1^\circ$C away from the true $9^\circ$C, it is not accurate.

Worked example (length). If your true height is exactly $5'9''$: measuring repeatedly with a yardstick and always getting $5'0''$ is consistent (precise) but wrong (not accurate); measuring with a laser yardstick and getting $5'9''$ every time is both correct (accurate) and consistent (precise). …