The purpose of this activity is define new types of units you need in your system. All attributes in use will have a unit connected. The system has a default set of units following the ISO standard. But you are also able to create new units. Examples of units are: Hours, Hz, MB, K, m/s, km/h etc.
For each unit you define you can also define derived units. For instance m/s is a derived unit from km/h. But in order to go from m/s to km/h you have to correct the value with a factor 3.6, i.e. m/s = 3.6 * km/h. If km/h is the unit and m/s is the derived attribute then the factor is 3.6. If m/s is the unit and km/h is the derived attribute then the factor is 0.2777.
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Units can be defined for attributes.