Document epoch.

[pspp] / spv-file-format.texi

diff --git a/spv-file-format.texi b/spv-file-format.texi
index dff235859b6f9b711dd3362abaf26c3e9a8d3a63..192c1c3ea1384534518ece495cbbb3536463cf56 100644 (file)
--- a/spv-file-format.texi
+++ b/spv-file-format.texi
@@ -901,7 +901,7 @@ X6 @result{}
     string[@t{command}] string[@t{subcommand}]
     string[@t{language}] string[@t{charset}] string[@t{locale}]
     (00 @math{|} 01) 00 (00 @math{|} 01) (00 @math{|} 01)
-    int
+    int[@t{epoch}]
     byte[@t{decimal}] byte[@t{grouping}]
     byte*8 01
     (string[@t{dataset}] string[@t{data file}] i0 int i0)?
@@ -918,6 +918,12 @@ such as @code{en_US.windows-1252} or @code{it_IT.windows-1252}.  The
 rest of the character strings in the member use this encoding.  The
 encoding string is itself encoded in US-ASCII.
 
+@code{epoch} is the year that starts the epoch.  A 2-digit year is
+interpreted as belonging to the 100 years beginning at the epoch.  The
+default epoch year is 69 years prior to the current year; thus, in
+2017 this field by default contains 1948.  In the corpus, @t{epoch}
+ranges from 1943 to 1948, plus some contain -1.
+
 @code{decimal} is the decimal point character.  The observed values
 are @samp{.} and @samp{,}.