What may happen if an instrument is not correctly set at zero?

Correct answer: A zero error may occur

The direct answer is option A: an incorrect zero setting can cause zero error. Before measuring, an instrument should show zero when no quantity is being measured, or it should be adjusted according to its instructions. If it does not, every reading may be shifted by a fixed amount or otherwise affected. For example, if a balance shows 2 g when empty, a later reading may include that unwanted offset unless it is corrected. The reasoning is: check the instrument at zero; notice any initial reading; correct or record the offset; then measure; interpret results while considering the error. Option A is correct because the fault is specifically called zero error. Option B is wrong because the sample itself does not become larger merely because the instrument is incorrectly set. Option C is wrong because an instrument setting does not automatically change the hypothesis. Option D is wrong because no instrument error can make an experiment repeat automatically. Memory cue: zero first, measure second.