Index: trunk/doc/pslib/psLibSDRS_Astrom.tex
===================================================================
--- trunk/doc/pslib/psLibSDRS_Astrom.tex	(revision 3069)
+++ trunk/doc/pslib/psLibSDRS_Astrom.tex	(revision 3176)
@@ -387,11 +387,15 @@
                             float exptime, float wavelength, const psObservatory *observatory);
 \end{verbatim}
-\subsubsection{SLALib information}
-
-SLALib requires several elements to perform the transformations
-between the tangent plane and the sky.  Pre-computing these quantities
-for each exposure means that subsequent transformations are faster.
-For historical reasons, this structure is known colloquially as
-``Wallace's Grommit''.
+
+\subsubsection{Environmental Information}
+
+A-priori astrometric transformations between the tangent plane and the
+sky require several pieces of information describing the current
+environmental conditions.  These quantities are consistent from image
+to image, and may vary only slowly with time.  Pre-computing these
+quantities for exposures means that subsequent transformations are
+faster.  The structure below carries the environment data of interest.
+For historical reasons, this structure is known colloquially as ``the
+Grommit''.
 
 \begin{verbatim}
@@ -459,5 +463,6 @@
 As such, it must be flexible, yet robust.  Accordingly, we will wrap
 the StarLink Astronomy Libraries (SLALib), which has already been
-developed.
+developed.  \tbd{SLAlib functions will be replaced in the next
+release}.
 
 \subsubsection{Coordinate frames}
@@ -482,6 +487,6 @@
 h(p,q,m,c)$, where $m$ and $c$ are the magnitude and color of the
 object, respectively; and
-\item TP $\longleftrightarrow$ Sky: SLALib transformation using a
-transform pre-computed for each pointing.
+\item TP $\longleftrightarrow$ Sky:  transformation to the sky using
+pre-computed coefficients for each pointing.
 \end{itemize}