Autodesk AUTOCAD 2006 Command Reference Manual page 390

Linear Dimensions
Sets the format and precision for linear dimensions.
Unit Format
Sets the current units format for all dimension types except Angular.
(DIMLUNIT system variable)
The relative sizes of numbers in stacked fractions are based on the DIMTFAC
system variable (in the same way that tolerance values use this system
variable).
Precision
Displays and sets the number of decimal places in the dimension text.
(DIMDEC system variable)
Fraction Format
Sets the format for fractions. (DIMFRAC system variable)
Decimal Separator
Sets the separator for decimal formats. (DIMDSEP system variable)
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