MicroStation's system for controlling units is very flexible, but it depends on knowing the true geometry size. Many of MicroStation's tools for dimensioning, placing cells, and referencing rely on the file units to work correctly. Unfortunately, MicroStation cannot always infer the file units in AutoCAD files. To accurately set the MicroStation Units options, you must understand the DWG file content and the standards used to create it.

AutoCAD uses two types of linear units that are specified by the LUNITS variable. DWG files with Engineering and Architectural units (LUNITS= 3 and 4) are implicitly English units (feet and inches), so their units are known. The other types — Scientific, Decimal, and Fractional (LUNITS = 1, 2, and 5, respectively) — do not imply a specific unit of measurement.

Beginning with AutoCAD 2000, INSUNITS system variable specifies units for Design Center blocks that are inserted into existing drawings. The INSUNITS variable allows for the type of automatic scaling that MicroStation performs when True Scaling is specified. Unfortunately, this variable does not exist in DWG files before AutoCAD 2000, and may be set inconsistently in files from more recent versions.

If the system variable INSUNITS is appropriately set, when you open the DWG file in MicroStation you can set the Units options to Design Center Units. This is the best way to ensure that units are consistent when you open a file in MicroStation.

To set the Design Center Units for a DWG file in MicroStation, use the DWG UNITS key-in to display the DWG/DXF Units dialog, which lets you control the Design Center Units (INSUNITS) setting. Use the Save Settings command (File > Save Settings) to save the units setting in the active design file.

If you do not set the Design Center Units, the Design Center Units that are saved to DWG are determined by the values for Working Units on the Design File Settings dialog, and/or Units on the Save As DWG/DXF Options dialog.