What should be done if repeated measurements give very different values?

Correct answer: The instrument and method should be checked

The direct answer is A: check the instrument and the method. Repeated measurements should usually be reasonably similar when the object and conditions have not changed. Very different readings may result from a faulty or unsuitable instrument, different reading positions, incorrect procedure, changing conditions, or recording mistakes. First inspect the instrument, its zero or calibration, the units, and the method; then repeat the measurement carefully and record all valid readings. Option A is correct because checking can locate the source of disagreement. Option B is wrong because choosing a favourite value introduces bias. Option C is wrong because deleting all values hides evidence. Option D is wrong because a conclusion should not be written before the problem is investigated. Rechecking is not failure; it is responsible scientific practice. Memory cue: unusual data means check, not choose.