Index: trunk/doc/release.2015/ps1.calibration/calibration.tex
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--- trunk/doc/release.2015/ps1.calibration/calibration.tex	(revision 39835)
+++ trunk/doc/release.2015/ps1.calibration/calibration.tex	(revision 39836)
@@ -436,7 +436,36 @@
 * result is a collection of zero points for photometric images
   * discuss stats on the zero points and the airmass terms
+* does eddie still use per exposure or per star airmass terms?
 \end{verbatim}
 
 \subsection{Relphot Analysis}
+
+The ubercal analysis above results in a table of zero points for all
+exposures considered to be photometric, along with a set of
+low-resolution flat-field corrections.  It is now necessary to use this
+information to determine zero points for the remaining exposures and
+to improve the resolution of the flat-field correction.  This analysis
+is done within the IPP DVO database system.
+
+The ubercal zero points and the flat-field correction data are loaded
+into the PV3 DVO database using the program \code{setphot}.  This
+program converts the reported zero point and flat field values to the DVO internal representation
+in which the zero point of each image is split into three main
+components:
+\[ 
+zp_{\rm total} = zp_{\rm nominal} + M_{cal} + K_{rm \lambda}(sec \zeta - 1)
+\]
+where $zp_{\rm nominal}$ is a static value for each filter, $K_{rm
+  \lambda}$ is the static slope of the trend with respect to the
+airmass trend ($\zeta$) for each filter, $M_{cal}$ is the offset
+needed by each exposure to match the ubercal value, or to bring the
+given image into agreement with the rest of the exposures, as
+discussed below.  The flat-field information is encoded in a table of
+flat-field offsets as a function of time, filter, and camera position.
+
+\note{measurement values are modified $M_{cal}, M_{flat}$, flags}
+
+When the ubercal values are ingested into the database, 
+
 \begin{verbatim}
 * ingest the ubercal zero points (setphot)