By default, the Calculator starts with the geodetic
coordinate system of WGS84 selected, or it will automatically recognize the coordinate system from specified input data. To select a system, double-click
on the blue box labeled System
in a Coordinate System area. 
Right-clicking on the blue System box also provides quick options for Select Coordinate System, Select Coordinate System by Map or choose Info to see details about the current system.
If this is the first time you have selected a coordinate
system you will be asked if you would like to Limit the Coordinate
Systems by geographic area. If you would like to be asked this each
time, check the Always Prompt
option. If you want your choice to be saved for all future system
selections uncheck this box. This setting can be modified in your
preferences at a later date,
as needed.
Selecting Yes will open the Coordinate
System Selection window. If you do not know the precise name
of the coordinate system you are looking for and would like to browse
the available coordinate systems for a specific area, you can define
a point or an area on this window using the Select
Coordinate System By Rectangle 
tool or
the Select Coordinate System
by Point 
tools found on the Coordinate
System Selection window's toolbar.
Selecting a coordinate system by rectangle will result in a list of
coordinate systems that contain
the boundaries of the polygon defined with the Select
Coordinate System By Rectangle tool. Selecting a coordinate
system by point will result in a list of coordinate systems that overlap with the point generated
using the Select Coordinate System
by Point tool. 
You may also use the Select Coordinate System By GeoCalc Polygon 
tool to import a polygon Area of Use from an object
defined in the Datasource. Clicking this tool will bring up a Select
Area of Use from GeoCalc Datasource Object dialog.
From this dialog, you may select one of several types of objects, including
specific Areas of Use, or Concatenated Transforms, Single Transforms,
or Coordinate Systems that have associated Areas of Use. Once you
have selected a particular object and click OK, the Area of Use associated
with that object will be imported into the Viewer and displayed atop
the world map, to be applied as the limiting polygon.
If you select OK after defining your selection or you choose No in
step 2 the Select Coordinate System from Datasource dialog will open.
In the Select Coordinate System dialog, coordinate systems are organized in the folder list on the left by type (Geodetic (Lat/Lon), Projected, Geocentric, Fitted, and String), continent, then by country and smaller political sub-units. If a coordinate system covers an entire continent, it will be found by clicking on the continent folder itself. Universal Transverse Mercator (UTM) systems are given their own top level groups. If you are unable to find your desired coordinate system, try using the search field at the bottom of the window. Once you have found and selected your desired coordinate system, click OK to return to the Job page.
Right click on the blue System box that lists the coordinate system to see additional options, including Copy, Paste or Swap source and target systems. There are also options to Export to File (*.prj, *.wkt, *.wkt2, *.gml) or View PRJ to see the WKT definition.
To use a Horizontal Time Dependent Positioning (HTDP) transformation, select the appropriate date for your data. Time-dependent transformations can be enabled or disabled in the General Preferences
To include vertical (height) data, double-click the Vertical box to select a vertical reference system.
Repeat this process to select the target coordinate system for the job, if applicable.