Any one of three length measuring devices may be used. The micrometer will permit the highest precision measurments but using one can be cumbersome, especially when reading the vernier scale. All methods will demonstrate the aforementioned objectives. Your instructor will give you guidance in choosing an appropriate measurement device. Always estimate tenths of the smallest division.
Some micrometers have verniers to assist the estimation.
You should also try the java vernier at java vernier . Experiment with one of the large verniers in the lab until you are sure you understand it. The vernier was invented 1631 by Pierre Vernier. Unclamp both top thumbscrews to permit moving caliper jaws. Open caliper to within a few mm of the dimension being measured.