When using Print Preparation, you can define and select from a list of Scales in the "Add Rectangular Viewport" command, separate from the Plot Scales defined by a Geospatial Administrator Schema or DGNLIB file.
The scales presented in the list and those available at placement time are defined by a Workspace variable pointing to an XML file containing the appropriate scales. If this variable is not defined or the file is not found then the software provides certain built-in scales. The scale value will be calculated by NumDgnUnits / NumPaperUnits. If the unit in PaperUnitName and DgnUnitName is different, the values will be converted to the same unit first.
MS_GEOXFM_BORDER_SCALE_DOMAINLIST_FILE XML file describing the scales for the project.
The file is of the format below.
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<Scales name="BorderScales">
<scale DisplayName="1"=400'" name="1in=400'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="4800.0" />
<scale DisplayName="1"=200'" name="1in=200'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="2400.0" />
<scale DisplayName="1"=100'" name="1in=100'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="1200.0" />
<scale DisplayName="1"=50'" name="1in=50'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="600.0" />
<scale DisplayName="1"=40'" name="1in=40'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="480.0" />
<scale DisplayName="1"=25'" name="1in=25'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="300.0" />
<scale DisplayName="1"=20'" name="1in=20'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="240.0" />
<scale DisplayName="1"=8'" name="1in=8'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="96.0" />
<scale DisplayName="1"=4'" name="1in=4'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="48.0" />
<scale DisplayName="1"=2'" name="1in=2'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="24.0" />
<scale DisplayName="1"=1'" name="1in=1'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="12.0" /></Scales>
This information is available in the Bentley Map Help documentation.