Unit of Measurement: A magnitude representing a physical quantity by use of a standard for measurement of that physical quantity.
Measuring Device: A piece of equipment used to measure a physical quantity based on a standard for measurement.
Measurement and Objectivity
Measurements are the most objective part of science because the resulting numbers are what they are. The mechanical devices used for measurement aide objectivity by removing the human factor that is human subjectivity. The validity of a measurement is only as valid as the theory behind it.