When placed into a liquid, the hydrometer bobs upright, and sinks to a certain level. The specific gravity or solution composition can be read from the liquid level on the vertical scale. The smallest detectable concentration an analytical instrument can determine at a given confidence level. Mass is a measure of the tendency of an object to resist acceleration. Measurement is the collection of quantitative data.
Measurement involves comparison of the quantity of interest with a standard called a unit.
The comparison is never perfect. As a result, measurements always include error. You must consider the reliability of the measurement when using it to make decisions or estimate other quantities. For example, 3.2 MJ is 3200000 J. meter. Compare with systematic error , random error and gross error .