}
+\dt \cw{-h} or \cw{--help}
+
+\dd Causes \cw{agedu} to print some help text and terminate
+immediately.
+
+\dt \cw{-V} or \cw{--version}
+
+\dd Causes \cw{agedu} to print its version number and terminate
+immediately.
+
\U OPTIONS
This section describes the various configuration options that affect
files in each directory, instead of just giving a combined report
for everything that's not in a subdirectory.
+The following option affects the text report mode \cw{-t}.
+
+\dt \cw{-a} \e{age} or \cw{--age} \e{age}
+
+\dd This option tells \cw{agedu} to report only files of at least the
+specified age. An age is specified as a number, followed by one of
+\cq{y} (years), \cq{m} (months), \cq{w} (weeks) or \cq{d} (days).
+(This syntax is also used by the \cw{-r} option.) For example, \cw{-a
+6m} will produce a text report which includes only files at least six
+months old.
+
The following options affect the stand-alone HTML generation mode
\cw{-H} and the text report mode \cw{-t}.
The argument to \cw{-r} consists of a single age, or two ages
separated by a minus sign. An age is a number, followed by one of
\cq{y} (years), \cq{m} (months), \cq{w} (weeks) or \cq{d} (days).
-The first age in the range represents the oldest data, and will be
-coloured red in the HTML; the second age represents the newest,
-coloured green. If the second age is not specified, it will default
-to zero (so that green means data which has been accessed \e{just
-now}).
+(This syntax is also used by the \cw{-a} option.) The first age in the
+range represents the oldest data, and will be coloured red in the
+HTML; the second age represents the newest, coloured green. If the
+second age is not specified, it will default to zero (so that green
+means data which has been accessed \e{just now}).
For example, \cw{-r 2y} will mark data in red if it has been unused
for two years or more, and green if it has been accessed just now.
\cw{rsync}(\e{1}) and \cw{make}(\e{1}). Such programs will fail to
update the atime of unmodified files despite depending on their
continued existence; a directory full of such files will be reported
-as disused by \cw{agedu} but deleting them will cause trouble.
+as disused by \cw{agedu} even in situations where deleting them will
+cause trouble.
+
+Finally, of course, \cw{agedu}'s normal usage mode depends critically
+on the OS providing last-access times which are at least approximately
+right. So a file system mounted with Linux's \cq{noatime} option, or
+the equivalent on any other OS, will not give useful results!
+(However, the Linux mount option \cq{relatime}, which distributions
+now tend to use by default, should be fine for all but specialist
+purposes: it reduces the accuracy of last-access times so that they
+might be wrong by up to 24 hours, but if you're looking for files that
+have been unused for months or years, that's not a problem.)
\U LICENCE