diff --git a/doc/sim65.sgml b/doc/sim65.sgml
index 2b99a6682..9f2914254 100644
--- a/doc/sim65.sgml
+++ b/doc/sim65.sgml
@@ -265,13 +265,13 @@ address range. Six values are currently defined:
 <p>Values $00 to $03 provide access to the latched (frozen) value of their respective live
 counters at the time of the last write to <tt>PERIPHERALS_COUNTER_LATCH</tt>.
 
-<p>When <tt>PERIPHERALS_COUNTER_LATCH</tt> equals $80, the <tt>PERIPHERALS_COUNTER_VALUE</tt>
-will be a 64-bit value corresponding to the number of nanoseconds elapsed since Midnight, Jan 1st,
-1970 UTC, at the time of the last latch operation.
+<p>When <tt>PERIPHERALS_COUNTER_SELECT</tt> equals $80, the <tt>PERIPHERALS_COUNTER_VALUE</tt>
+will be a 64-bit value corresponding to the number of nanoseconds elapsed since the Unix epoch
+(Midnight, Jan 1st, 1970 UTC), at the time of the last latch operation.
 
-<p>When <tt>PERIPHERALS_COUNTER_LATCH</tt> equals $81, the high 32 bits of <tt>PERIPHERALS_COUNTER_VALUE</tt>
-will be a 32-bit value corresponding to the number of seconds elapsed since Midnight,
-Jan 1st, 1970 UTC, at the time of the last latch operation. The low 32 bits of
+<p>When <tt>PERIPHERALS_COUNTER_SELECT</tt> equals $81, the high 32 bits of <tt>PERIPHERALS_COUNTER_VALUE</tt>
+will be a 32-bit value corresponding to the number of seconds elapsed since the Unix epoch (Midnight, Jan 1st,
+1970 UTC), at the time of the last latch operation. The low 32 bits of
 <tt>PERIPHERALS_COUNTER_VALUE</tt> will hold the nanoseconds since the start of that second.
 
 <p>The two different wallclock-time latch registers will always refer to precisely the same time instant.
@@ -279,10 +279,10 @@ For some applications, the single 64-bit value measured in nanoseconds will be m
 for other applications, the split 32/32 bits representation with separate second and nanosecond
 values will be more convenient.
 
-<p>Note that the definition above, with time elapsed measured since Midnight, Jan 1st, 1970 UTC, is
-an approximation, as the implementation depends on the way POSIX definition time. Unfortunately,
-POSIX does not account for leap seconds; it incorrectly assumes that all days are precisely 86400 seconds
-long.
+<p>Note that the time elapsed since the Unix epoch is an approximation, as the implementation depends on the
+way POSIX defines time-since-the-epoch. Unfortunately, POSIX incorrectly assumes that all days are precisely
+86400 seconds long, which is not true in case of leap seconds. The way this inconsistency is resolved is
+system dependent.
 
 <p>On reset, <tt>PERIPHERALS_COUNTER_SELECT</tt> is initialized to zero. If the <tt>PERIPHERALS_COUNTER_SELECT</tt>
 register holds a value other than one of the six values described above, all <tt>PERIPHERALS_COUNTER_VALUE</tt>