Index: /trunk/doc/release.2015/inputs/lib.bib
===================================================================
--- /trunk/doc/release.2015/inputs/lib.bib	(revision 41188)
+++ /trunk/doc/release.2015/inputs/lib.bib	(revision 41189)
@@ -16685,2 +16685,16 @@
 }
 
+@article{10.2307/2345503,
+ ISSN = {00359246},
+ URL = {http://www.jstor.org/stable/2345503},
+ abstract = {The scope of application of iteratively reweighted least squares to statistical estimation problems is considerably wider than is generally appreciated. It extends beyond the exponential-family-type generalized linear models to other distributions, to non-linear parameterizations, and to dependent observations. Various criteria for estimation other than maximum likelihood, including resistant alternatives, may be used. The algorithms are generally numerically stable, easily programmed without the aid of packages, and highly suited to interactive computation.},
+ author = {P. J. Green},
+ journal = {Journal of the Royal Statistical Society. Series B (Methodological)},
+ number = {2},
+ pages = {149--192},
+ publisher = {[Royal Statistical Society, Wiley]},
+ title = {Iteratively Reweighted Least Squares for Maximum Likelihood Estimation, and some Robust and Resistant Alternatives},
+ volume = {46},
+ year = {1984}
+}
+
Index: /trunk/doc/release.2015/ps1.calibration/calibration.tex
===================================================================
--- /trunk/doc/release.2015/ps1.calibration/calibration.tex	(revision 41188)
+++ /trunk/doc/release.2015/ps1.calibration/calibration.tex	(revision 41189)
@@ -115,5 +115,5 @@
 bright-star systematic error floor for individual astrometric
 measurements is 16 milliarcseconds.}  \textmod{The Pan-STARRS Data Release 2
-(DR2) astrometry is tied to the Gaia DR1 coordinate frame with a
+(DR2) astrometric system is tied to the Gaia DR1 coordinate frame with a
 systematic uncertainty of $\sim 5$ milliarcseconds.}
 \end{abstract}
@@ -132,5 +132,5 @@
 Type Ia supernovae to measure the history of the expansion of the
 universe.  The majority of the time (56\%) was spent on surveying the
-$\frac{3}{4}$ of the sky north of $-30$ Declination with
+$\frac{3}{4}$ of the sky north of $-30\degree$ Declination with
 \grizy\ filters in the so-called $3\pi$ Survey.  Another $\sim 25\%$
 of the time was concentrated on repeated deep observations of 10
@@ -571,5 +571,5 @@
 derived from the projection of the reference coordinates.  One caveat
 is that the chip reference coordinates are also degenerate with the
-fitted distortion.  In order to avoid being sensitive to the exact
+fitted distortion.  \textmod{To avoid} being sensitive to the exact
 positions of the chips at this stage, we measure the local gradient
 between the focal plane and tangent plane coordinate systems.  We then
@@ -635,7 +635,6 @@
 \begin{itemize}
 \item \code{ZPT_REF} : the nominal zero point for this filter
-\item \code{ZPT_OBS} : the measured zero point for this chip /
-  exposure
-\item \code{ZPT_ERR} : the measured error on \code{ZPT_OBS}
+\item \code{ZPT_OBS} : the measured zero point for this chip / exposure
+\item \code{ZPT_ERR} : the standard deviation of \code{ZPT_OBS}
 \item \code{ZPT_NREF} : the number of stars used to measure \code{ZPT_OBS}
 \item \code{ZPT_MIN} : minimum reference magnitude included in analysis
@@ -663,9 +662,9 @@
 
 The master DVO database is used to perform the full photometric and
-astrometric calibration of the data.  During these analysis steps, a
-wide variety of conditions are noted for individual measurements, for
-the objects (either as a whole or for specific filters) and for the
-images.  A set of bit-valued flags are used in the database to record
-these conditions.
+astrometric calibration of the \textmod{PS1} data.  During these
+analysis steps, a wide variety of conditions are noted for individual
+measurements, for the objects (either as a whole or for specific
+filters) and for the images.  A set of bit-valued flags are used in
+the database to record these conditions.
 %
 Table~\ref{tab:measure_mask_values} lists the flags specific to
@@ -868,5 +867,8 @@
 calibrations.
 
-Photometric nights are selected and all other exposures are ignored.
+In this first stage, the goal is to determine an initial
+highly-reliable collection of zero points for exposures without any
+confounding systematic error sources.  To this end, only 
+photometric nights are selected and all other exposures are ignored.
 Each night is allowed to have a single fitted zero point
 (corresponding to the sum $zp_{\rm ref} + M_{cal}$ below) and a single
@@ -882,5 +884,6 @@
 \cite{2012ApJ...756..158S} determined flat-field corrections for
 $2\times 2$ sub-regions of each chip in the camera and four distinct
-time periods (``seasons'').  Later analysis (PV2) used an $8\times8$
+time periods (``seasons''), ranging from as short as one month to nearly
+15 months.  Later analysis (PV2) used an $8\times8$
 grid of flat-field corrections to good effect.
 
@@ -1016,8 +1019,9 @@
 corrections are applied to each of the types of measurements stored in
 the database, PSF, Aperture, Kron.  The calibration math remains the
-same regardless of the kind of magnitude being measured.  Also note
-that for the moment, this discussion should only be considered as
-relevant to the chip measurements.  Below we discuss the implications
-for the stack and warp measurements.
+same regardless of the kind of magnitude being measured \textmod{(see
+  however Section~\ref{sec:phot.stack} for the difference in the stack
+  calibration)}.  Also note that for the moment, this discussion
+should only be considered as relevant to the chip measurements.  Below
+we discuss the implications for the stack and warp measurements.
 
 When the ubercal zero points and flat-field data are loaded,
@@ -1105,10 +1109,10 @@
 
 Similarly for images, we exclude those with more than 2 magnitudes of
-extinction or for which the deviation greater of the zero points per
-star are than 0.075 mags or 2$\times$ the median value, whichever is
-greater.  These cuts are somewhat conservative to limit us to only
-good measurements.  The images and stars rejected above are not used
-to calculate the system of zero points and mean magnitudes.  These
-cuts are updated several times as the iterations proceed.  After the
+extinction or for which the standard deviation of the zero points are
+more than 0.075 mags or 2$\times$ the median value, whichever is greater.
+These cuts are somewhat conservative to limit us to only good
+measurements.  The images and stars rejected above are not used to
+calculate the system of zero points and mean magnitudes.  These cuts
+are updated several times as the iterations proceed.  After the
 iterations have completed, the images which have been reject are
 calibrated based on their overlaps with other images.
@@ -1233,5 +1237,5 @@
 they wait for the data they need to receive from their neighbors.  The
 management of this stage is performed by communication between the
-region host.  At the end of the iterations, the regions hosts write out
+region hosts.  At the end of the iterations, the regions hosts write out
 their final image calibrations.  The master machine then loads the
 full set of image calibrations and then applies these calibrations
@@ -1275,5 +1279,19 @@
 data in DVO after the initial relphot calibration to measure the
 flat-field residual with much finer resolution: 124 x 124 flat-field
-values for each GPC1 chip (40x40 pixels per point).  We then used
+values for each GPC1 chip (40x40 pixels per point).  \textadd{For this
+  analysis, we did not use the entire database, but instead extracted
+  relatively bright, but unsaturated measurements (instrumental
+  magnitudes between -10.5 and -14.5) for stars with at least 8
+  measurements, including 3 used to measure the average photometry in
+  the corresponding filter.  These measurements were extracted from a
+  collection of 10 sky regions in both low and high-stellar density
+  regions covering a total of $\sim 5800$ square degrees of sky.
+  Unlike the lower-resolution photometric flat-fields determined in
+  the ubercal analysis, the photometric flat-fields calculated in this
+  analysis are static in time; they supplement the flats from the
+  ubercal analysis.  A total of 1.95 billion measurements were
+  extracted for this analysis.
+
+We then used
 \ippprog{setphot} to apply this new flat-field correction, as well as the
 ubercal flat-field corrections, to the data in the database.  At this
@@ -1563,5 +1581,5 @@
 the modified weight is less than 30\% of the median weight
 ($\omega^\prime < 0.3 <\omega>$) then the point is treated as clipped.
-The $\chi^2$ is determined from the {\em unclipped} points using the
+The $\chi^2$ is determined from the \textadd{remaining} {\em unclipped} points using the
 standard Poisson errors.  Data points which are so excluded are marked
 with bit-flags: \code{ID_MEAS_MASKED_PSF},
@@ -1570,5 +1588,5 @@
 
 Bootstrap-resampling analysis is used to assess the errors on the fit
-parameters: A number of measurements equal to the number of {\em
+parameters: A number of measurements equal to the number of remaining {\em
   unclipped} data points are randomly selected from the set of
 unclipped data points, with replacement after each selection.  These
@@ -1874,5 +1892,5 @@
 position across the sky.  For each pixel in these images, we selected
 all objects with (14.5, 14.5, 14.5, 14.0, 13.0) $<$ ($g,r,i,z,y$) $<$
-(17, 17, 17, 16.5, 15.5), with at least 3 measurements in $i$-band (to
+(17, 17, 17, 16.5, 15.5) magnitudes, with at least 3 measurements in $i$-band (to
 reject artifacts detected in a pair of exposures from the same night),
 with \code{PSF_QF} $> 0.85$ (to reject excessively-masked objects),
@@ -3028,4 +3046,6 @@
 community.
 
+\note{need to add discussion of SDSS, DES, LSST, Gaia}
+
 \acknowledgments