title: Is user + sys time equal to real/wall clock time?
body: <p>In Perl:</p>
  
  <pre><code>my ($usr,$sys,$cusr,$csys) = times;
  printf "real %s, user %s, sys %s\n", $usr + $sys, $usr, $sys;
  </code></pre>
  
  <p>Is this true?  I read some other questions where people did things like saving the current time away in a variable and collecting it later, but why wouldn't this work?</p>