eggert mod

SCCS-file: leapseconds
SCCS-SID: 7.5

leapseconds

@@ -2,6 +2,14 @@
 
 # Allowance for leapseconds added to each timezone file.
 
+# The International Earth Rotation Service periodically uses leap seconds
+# to keep UTC to within 0.9 s of TAI (atomic time); see
+# Terry J Quinn, The BIPM and the accurate measure of time,
+# Proc IEEE 79, 7 (July 1991), 894-905.
+# There were no leap seconds before 1972, because the official mechanism
+# accounting for the discrepancy between atomic time and the earth's rotation
+# did not exist until the early 1970s.
+
 # The correction (+ or -) is made at the given time, so lines
 # will typically look like:
 #	Leap	YEAR	MON	DAY	23:59:60	+	R/S