unit

<unit>

A unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same physical quantity. Any other value of the physical quantity can be expressed as a simple multiple of the unit of measurement. For example, length is a physical quantity, and metre is a unit of length that represents a definite predetermined length.

The node <units> in the *.spd file can be used to change some defaults or to add specialized units, which in principle are not supported. The structure and contents of this subtree <units> requires to have the format as further detailed in this document. The following attributes are available:

• n - name
• pn - printed name (decorated and translated)
• p - Priority of the unit, it is regarded as more important than others units. The possible values for 'p' are 1, 2 and 3, as follows,

1 - It gives maximum priority, and therefore a unit with p="1" is the default unit in the GUI.
2 - A unit with p="2" is always shown in the combobox of below to facilitate the selection of the most used units.
3 - It gives lowest priority, and therefore a unit with p="3" could only be chosen when clicking on 'More units...' option in the combobox of below, which enables the user to choose the unit from a table.

• factor - The conversion factor used to multiply a quantity when converting from one system of units to another. It is the mathematical tool for converting between units of measurement [1 unit=factor*unit(SI)]. Example: 1mm=10e-3 m.
• help - To make easier to the user to identify the unit.

Example of <units> field: Species concentration and reference variable are not supported and therefore, both magnitudes are defined in the *.spd file, as follows,

<units>
<unit_magnitude n="Reference_variable_unit" pn="Reference variable unit" default="U" SI_base="U" active="1">
      <unit n="U" pn="ReferenceUnit" p="2" factor="1.0"/>
      <unit n="ppm" pn="parts-per-million" p="2" factor="1.0e-6" help="parts-per-million"/>
      <unit n="ppb" pn="parts-per-billion" p="2" factor="1.0e-9" help="parts-per-billion"/>
      <unit n="%" pn="per-one-hundred" p="2" factor="0.01" help="per-one-hundred"/>
      <unit n="%0" pn="per-one-thousand" p="2" factor="0.001" help="per-one-thousand"/>
      <unit n="Np" pn="Nepper" p="2" factor="1.0" help="Nepper"/>
   </unit_magnitude>
<unit_magnitude n="Species_concentration" pn="Species concentration" default="C" SI_base="C" active="1">
      <unit n="C" pn="ReferenceUnit" p="2" factor="1"/>
      <unit n="ppm" pn="parts-per-million" p="2" factor="1.0e-6" help="parts-per-million"/>
      <unit n="ppb" pn="parts-per-billion" p="2" factor="1.0e-9" help="parts-per-billion"/>
      <unit n="%" pn="per-one-hundred" p="2" factor="0.01" help="per-one-hundred"/>
      <unit n="%0" pn="per-one-thousand" p="2" factor="0.001" help="per-one-thousand"/>
      <unit n="mol" pn="mole" p="2" factor="1.0"/>
    </unit_magnitude>
</units>