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====== Units ======

In Ecolego it is not necessary to specify units for each object. This entry is optional. However, the user should specify the unit of the simulation time step and [[Material|materials]] (if [[Material|materials]] are included in the [[Model|model]]) before starting a simulation. The default unit for the simulation time step is **Year** but can be changed in the [[Simulation_settings|simulation settings window]].

===== Entering units =====

Units are specified in the [[Editing_properties|properties page]] when editing [[Block|blocks]]. Some objects like [[Compartment|compartments]] and [[Transfer|transfers]] cannot be assigned units because they are implicit from the materials and time unit of the model. For instance, if the unit for the material “Arsenic” is set to “kg” and the simulation time unit is set to “year”, the unit of a compartment will be (kg) and the unit of a transfer will be (kg/year).

Use ^ to enter exponents, for example: m^2 s^-1 will be displayed as (m<sup>2</sup> s<sup>-1</sup>)

==== Unit suffix ====

To specify unit notations such as “freshweight” or “particle” you can use a ”.”. For example: kg.fw will be displayed as (kg<sub>fw</sub>).

The unit suffix is important for unit checking, see below.

===== Unit conversions =====

There is no automatic [[constants_editing_tool|unit conversion]] in Ecolego. 
===== Unit checking =====

By default Ecolego will not perform unit checking. To enable this feature, open the errors and warnings page of the [[Preferences|preferences]] screen.

The unit checking algorithm is strict - there might be cases (for instance with empirical relationships) where the unit checker will report an error even if there is none. Also, when using suffixes, the unit checking algorithm will refuse to accept mixing of quantities. For instance, the expression rho(kg/m<sup>3</sup>) = m (kg<sub>part</sub>)/V(m<sup>3</sup>) will fail because kg != kg<sub>part</sub>.

===== Radionuclides =====

The default unit for radionuclides is **Bq**. The unit must be the same for all radionuclides, so when the unit is changed from **Bq** to **mol** for one radionuclide the unit of all other radionuclides will change.

===== Built-in units =====

**Bq**;
**s**;
**year^-1**;
**min**;
**h**;
**d**;
**week**;
**month**;
**year**;
**mol**.
===== See also =====

  * [[Expression_syntax|Expression syntax]]
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