--- libev/ev.pod	2007/11/12 08:32:52	1.11
+++ libev/ev.pod	2007/11/12 08:35:18	1.12
@@ -546,7 +546,7 @@
 
 This doesn't mean there will always be 3600 seconds in between triggers,
 but only that the the callback will be called when the system time shows a
-full hour (UTC), or more correct, when the system time is evenly divisible
+full hour (UTC), or more correctly, when the system time is evenly divisible
 by 3600.
 
 Another way to think about it (for the mathematically inclined) is that
@@ -561,8 +561,11 @@
 current time as second argument.
 
 NOTE: I<This callback MUST NOT stop or destroy the periodic or any other
-periodic watcher, ever, or make any event loop modificstions>. If you need
-to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
+periodic watcher, ever, or make any event loop modifications>. If you need
+to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.
+
+Also, I<<this callback must always return a time that is later than the
+passed C<now> value >>. Not even C<now> itself will be ok.
 
 Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
 ev_tstamp now)>, e.g.: