Similar to print format, but used by the @cmd{WRITE} command
(@pxref{WRITE}).
+@cindex measurement level
+@item Measurement level
+@anchor{Measurement Level}
+One of the following:
+
+@table @asis
+@item Nominal
+Each value of a nominal variable represents a distinct category. The
+possible categories are finite and often have value labels. The order
+of categories is not significant. Political parties, US states, and
+yes/no choices are nominal. Numeric and string variables can be
+nominal.
+
+@item Ordinal
+Ordinal variables also represent distinct categories, but their values
+are arranged according to some natural order. Likert scales, e.g.@:
+from strongly disagree to strongly agree, are ordinal. Data grouped
+into ranges, e.g.@: age groups or income groups, are ordinal. Both
+numeric and string variables can be ordinal. String values are
+ordered alphabetically, so letter grades from A to F will work as
+expected, but @code{poor}, @code{satisfactory}, @code{excellent} will
+not.
+
+@item Scale
+Scale variables are ones for which differences and ratios are
+meaningful. These are often values which have a natural unit
+attached, such as age in years, income in dollars, or distance in
+miles. Only numeric variables are scalar.
+@end table
+
+Variables created by @cmd{COMPUTE} and similar transformations,
+obtained from external sources, etc., initially have an unknown
+measurement level. Any procedure that reads the data will then assign
+a default measurement level. @pspp{} can assign some defaults without
+reading the data:
+
+@itemize @bullet
+@item
+Nominal, if it's a string variable.
+
+@item
+Nominal, if the variable has a WKDAY or MONTH print format.
+
+@item
+Scale, if the variable has a DOLLAR, CCA through CCE, or time or date
+print format.
+@end itemize
+
+Otherwise, @pspp{} reads the data and decides based on its
+distribution:
+
+@itemize @bullet
+@item
+Nominal, if all observations are missing.
+
+@item
+Scale, if one or more valid observations are noninteger or negative.
+
+@item
+Scale, if no valid observation is less than 10.
+
+@item
+Scale, if the variable has 24 or more unique valid values. The value
+24 is the default and can be adjusted (@pxref{SET SCALEMIN}).
+@end itemize
+
+Finally, if none of the above is true, @pspp{} assigns the variable a
+nominal measurement level.
+
@cindex custom attributes
@item Custom attributes
User-defined associations between names and values. @xref{VARIABLE