diff -r f76d49b98a1c css3-transforms/Transforms.src.html
--- a/css3-transforms/Transforms.src.html	Tue Mar 13 11:19:47 2012 -0700
+++ b/css3-transforms/Transforms.src.html	Tue Mar 13 14:27:26 2012 -0700
@@ -380,10 +380,37 @@
               </div>
 
               <p>
-                The '<code class="property">perspective</code>' and '<code class="property">perspective-origin</code>'
+                The 'perspective' and 'perspective-origin'
                 properties can be used to add a feeling of depth to a scene by making elements higher on the Z axis
-                (closer to the viewer) appear larger, and those further away to appear smaller.
+                (closer to the viewer) appear larger, and those further away to appear smaller. The scaling is proportional
+                to d/(d-Z) where d, the ‘perspective(<length>)’, is the distance from the drawing plane to the the assumed
+                position of the viewer's eye.
               </p>
+              
+              <div class="figure"> <img alt="Diagram of scale vs. Z position" src="perspective_distance.png">
+                <p class="caption">Diagrams showing how scaling depends on the
+              	 ‘perspective’ property and Z position. In the top diagram, Z is
+              	 half of d. In order to make it appear that the original
+              	 circle (solid outline) appears at Z (dashed circle) the
+              	 circle is scaled up by a factor of two resulting in the light
+              	 blue circle. In the bottom diagram the circle is scaled down
+              	 by a factor of one-third to make it appear behind the original
+              	 position.
+                </p>
+              </div>
+              
+              <p>Normally the assumed position of the viewer's eye is centered on
+                a drawing. This position can be moved if desired (for example
+                if a web page contains multiple drawings that should share a common
+                perspective) by setting ‘perspective-origin’.
+              </p>
+              
+              <div class="figure"> <img alt="Diagram of different perspective-origin" src="perspective_origin.png">
+                <p class="caption">
+                  Diagram showing the effect of moving the perspective origin upward.
+                </p>
+              </div>
+              
               <p id="perspective-matrix-computation">
                 The <a href="#TermPerspectiveMatrix"><i>perspective matrix</i></a> is computed as follows:
                 <!-- Make this more mathy, with matrices? -->
@@ -395,6 +422,20 @@
                 </ol>
               </p>
               
+              <p>
+                The resulting matrix is:
+              </p>
+              
+              <div class="figure">
+                <img alt="\begin{bmatrix}  1 &amp; 0 &amp; -x_p/d &amp; 0 \\  0 &amp; 1 &amp; -y_p/d &amp; 0 \\  0 &amp; 0 &amp; 1 &amp; 0 \\  0 &amp; 0 &amp; -1/d &amp; 1 \end{bmatrix}" src="perspective_origin_equation.png">
+              </div>
+              
+              <p>where x<sub>p</sub> and y<sub>p</sub> are the computed values of ‘perspective-origin’
+                and d is the length provided by  the value of the ‘perspective’ property.
+              </p>
+              
+              <div class="issue">Isn't this missing the scaling factor d/(d-Z).</div>
+              
               <div class="example">
                 <p>This example shows how perspective can be used to cause three-dimensional transforms to appear more realistic.
                 </p>