Index: /trunk/doc/pslib/psLibADD.tex
===================================================================
--- /trunk/doc/pslib/psLibADD.tex	(revision 1703)
+++ /trunk/doc/pslib/psLibADD.tex	(revision 1704)
@@ -1,3 +1,3 @@
-%%% $Id: psLibADD.tex,v 1.39 2004-09-07 19:51:08 price Exp $
+%%% $Id: psLibADD.tex,v 1.40 2004-09-07 23:20:09 price Exp $
 \documentclass[panstarrs]{panstarrs}
 
@@ -1235,7 +1235,19 @@
 \alpha_p & = & 0^\circ \\
 \delta_p & = & 23^\circ27'8''.26 - 46''.845\, T - 0''.0059\, T^2 + 0''.00181\, T^3 \\
-\phi_p & = & 0^\circ \\
-\end{eqnarray}
-where $T$ is the time in \tbr{Julian} centuries since 1900.
+\phi_p & = & 0^\circ
+\end{eqnarray}
+where $T$ is the time in Julian centuries since 1900.
+
+\paragraph{Precession}
+
+The appropriate values, from Elixir, are:
+\begin{eqnarray}
+\alpha_p & = & 90^\circ - (0^\circ.6406161\, T + 0^\circ.0000839\, T^2 + 0^\circ.0000050\, T^3) \\
+\delta_p & = & 0^\circ .5567530\, T - 0^\circ.0001185\, T^2 - 0^\circ.0000116\, T^3 \\
+\phi_p & = & 90^\circ + 0^\circ.6406161\, T + 0^\circ.0003041\, T^2 + 0^\circ.0000051\, T^3
+\end{eqnarray}
+where $T$ is $($MJD$_{\rm out} -$ MJD$_{\rm in})/36525$ is the difference
+between the two epochs, in Julian centuries.
+
 
 \paragraph{Suggested test cases}
@@ -1254,4 +1266,9 @@
 coordinates at J2100.0 (i.e., $T=2$), $(\lambda,\beta) =
 (167.072470^\circ,27.308813^\circ)$.
+
+For each of the above input coordinates, precessing from J2100 to
+J1900 gives the following output coordinates:
+$(357.437^\circ,-1.113^\circ)$, $(358.719^\circ,88.886^\circ)$ and
+$(177.423^\circ,31.113^\circ)$.
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%