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For some data formats an external unit is not defined in the file to be imported. This elements The element <externUnit> allows the unit to be specified explicitly. This unit , which is then used in to find the corresponding unit conversions that are as configured in a UnitConversion UnitConversionsFiles (see see 02 Unit Conversions).

<externUnit parameterId="P.nwp.fcst" unit="mm" cumulativeSum="false"/>

Attributes ;of <externUnit>:

• parameterId: Id of the parameter for which a unit is specified. This is the internal parameter Id.
• unit: specification of unit. This unit must be available in the UnitConversions specified in the unitConversionsId element.
• cumulativeSum:  if this option is set to "true", then it is possible to receive the parameters as cumulative sums. Cumulative sums are partial sums of a given sequence of numbers. For example, if the sequence is:  {a, b, c, d, ...}, then the cumulative sums are: a, a+b, a+b+c, a+b+c+d, .... . The import module will then calculate the values for the individual time steps {a, b, c, d, ...} by subtracting the cumulative sum of the previous cumulative sum value.
• cumulativeMean: similar to cumulativeSum, if cumulativeMean is set to "true", then it is possible to receive the parameters as cumulative means. Cumulative means are partial means of a given sequence of numbers. Therefore, for a given sequence of numbers s = {x₁,x₂,...,x_n,x_n+1} cumulative means are calculated as follows: CM (x_n+1) = [x_n+1 + n * CM (x_n)] ⁄ n+1. The import module will then calculate the values for the individual time steps {a, b, c, d, ...} by multiplying the cumulative mean with the amount of time steps already processed and then subtracting of the previous value that has been also multiplied with the amount of timestep processed minus 1.

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