Define 'relative high resolution time'

Fixes w3c#87

index.html

@@ -250,9 +250,21 @@ <h3>Time Origin</h3>
     recorded with respect to a global monotonic clock that is not subject to
     system and user clock adjustments, clock skew, and so on—see <a href=
     "#sec-monotonic-clock"></a>.</p>
-    <p>The <dfn data-export="">current high resolution time</dfn> is the high
-    resolution time from the <a>time origin</a> to the present time (typically
-    called "now").</p>
+    <p>
+    <div algorithm="relative high resolution time">
+      The <dfn data-export="">relative high resolution time</dfn> given |time|,
+       a {{DOMHighResTimeStamp}}, and |global|, a [=Realm/global object=],
+       runs the following steps:
+       <ul>
+         <li>Let |diff| be the difference between |time| and the |global|'s <a>time origin</a>.</li>
+         <li>Return |diff|.</li>
+       </ul>
+    </div>
+    </p>
+    <p>The <dfn data-export="">current high resolution time</dfn> returns the 
+    result of <a>relative high resolution time</a> where <i>time</i> is the 
+    present time and <i>global</i> is the <a data-cite="DOM#context-object">
+    context object</a>'s relevant [=Realm/global object=].</p>
   </section>
   <section id="sec-domhighrestimestamp">
     <h3>The <dfn data-export="">DOMHighResTimeStamp</dfn> typedef</h3>