@c PSPP - a program for statistical analysis.
-@c Copyright (C) 2017 Free Software Foundation, Inc.
+@c Copyright (C) 2017, 2020 Free Software Foundation, Inc.
@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3
@c or any later version published by the Free Software Foundation;
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
@cindex @code{$DATE}
@item $DATE
Date the @pspp{} process was started, in format A9, following the
-pattern @code{DD MMM YY}.
+pattern @code{DD-MMM-YY}.
+
+@cindex @code{$DATE11}
+@item $DATE11
+Date the @pspp{} process was started, in format A11, following the
+pattern @code{DD-MMM-YYYY}.
@cindex @code{$JDATE}
@item $JDATE
@item
Except in scientific notation, a decimal point is included only when
it is followed by a digit. If the integer part of the number being
-output is 0, and a decimal point is included, then the zero before the
-decimal point is dropped.
+output is 0, and a decimal point is included, then @pspp{} ordinarily
+drops the zero before the decimal point. However, in @code{F},
+@code{COMMA}, or @code{DOT} formats, @pspp{} keeps the zero if
+@code{SET LEADZERO} is set to @code{ON} (@pxref{SET LEADZERO}).
In scientific notation, the number always includes a decimal point,
even if it is not followed by a digit.