Documentation clarifications for now/0 and timer:tc/3

erts/doc/src/erlang.xml

@@ -2767,8 +2767,10 @@ os_prompt%</pre>
           Otherwise, some other point in time is chosen. It is also
           guaranteed that subsequent calls to this BIF returns
           continuously increasing values. Hence, the return value from
-          <c>now()</c> can be used to generate unique time-stamps. It
-          can only be used to check the local time of day if
+          <c>now()</c> can be used to generate unique time-stamps,
+          and if it is called in a tight loop on a fast machine
+          the time of the node can become skewed.</p>
+        <p>It can only be used to check the local time of day if
           the time-zone info of the underlying operating system is
           properly configured.</p>
       </desc>

lib/stdlib/doc/src/timer.xml

@@ -211,7 +211,8 @@
       </type>
       <desc>
         <p>Evaluates <c>apply(Module, Function, Arguments)</c> and measures
-          the elapsed real time. Returns <c>{Time, Value}</c>, where 
+          the elapsed real time as reported by <c>now/0</c>.
+          Returns <c>{Time, Value}</c>, where 
           <c>Time</c> is the elapsed real time in <em>microseconds</em>,
           and <c>Value</c> is what is returned from the apply.</p>
       </desc>