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UnitsManager (hwx.inspire.core)
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Manages the various unit systems used throughout the application.

- gui     - for displaying/setting numeric values in the gui.
- solver  - for converting numbers when exporting to a solver.
- current - the system used when setting/getting attribute values.

There is one gui unit system used throughout Inspire.
Its system can be set either via the settings dialog or the popup menu
on the main window. All numeric gui values are displayed/entered using
these units.

The solver units are used when exporting the model to a solver.
Every time you ask for the solver units you get a new unit system with
its system set from the value in settings.

setting/getting numeric values is 'current units'. Aware
when you call part.mass the value is multiplied the the current units
as defined by this class. The current units are specified using the
usingUnits context method current units can be:

  - base
  - gui
  - solver
  - any system, like MKS, IPS, MPA, ...

----------
Properties
----------

  +----------+----------+----------+
  | current_ | gui_     | solver_  |
  +----------+----------+----------+

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Public Methods
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  +----------------------------+
  | getUnits_ (self, system)   |
  +----------------------------+
  | usingUnits_ (self, system) |
  +----------------------------+

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Property Details
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.. _current:
.. method:: current

Returns the current unit system.

Returns:
  Units : The current unit system.

.. _gui:
.. method:: gui

The common.Units manager displayed in the gui.
    

.. _solver:
.. method:: solver

The common.Units manager used for exporting to MotionSolve.
    

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Method Details
--------------

.. _getUnits:
.. method:: getUnits(self, system)

Returns a common.Units manager for the passed system name.

:param system: Can be base, gui, solver,
            any system like MKS, IPS, MPA, CGS,...
:type system: str

:returns: The units system specified by system.
:rtype: Units


.. _usingUnits:
.. method:: usingUnits(self, system)

Context to specify the current units.

:param system: System can be

            - base : always SI units, internal units of the data model, this is default.
            - gui : user specified gui units and angle=deg, ang_velocity=rpm.
            - solver : "Model units" from preferences and angle=rad.
            - any unit system: "MKS", "MMKS", "IPS, "MPA", ...
:type system: str