Which reading is more reliable, with a metric ruler or a vernier caliper? why?
The vernier caliper may be more reliable than a metric ruler. This is because the vernier caliper has a special calibrated scale, which has markings that enable you to correctly determine tenths of a millimeter or hundredths of an inch.
The caliper is calibrated. That means, if calibrated properly, it is accurate. Where as a ruler could be off. You use a caliper when you need exact, exact measurements