Index: trunk/doc/release.2015/systematics.20140411/diffusion.tex
===================================================================
--- trunk/doc/release.2015/systematics.20140411/diffusion.tex	(revision 40302)
+++ trunk/doc/release.2015/systematics.20140411/diffusion.tex	(revision 40303)
@@ -308,16 +308,19 @@
 grid of images of a dense stellar field.  The purpose of this second
 step is to correct the basic flat-field image for errors arising from
-the non-uniformity of the illumination, from non-pixel uniformity due
-to the varying optical distorition across the field, and any other
-factors which may make the flat-field image inconsistent with stellar
-photometry, e.g., SED, filter band-pass variations, etc
+the non-uniformity of the illumination, from \newtext{variations in
+  the effective pixel size} \oldtext{non-pixel uniformity} due to the
+varying optical \newtext{distortion} \oldtext{distorition} across the
+field, and any other factors which may make the flat-field image
+inconsistent with stellar photometry, e.g., SED, filter band-pass
+variations, etc
 \citep[see][]{waters2017,2004PASP..116..449M,2007ASPC..364..153M}.
-This correction was made on a relatively coarse grid across the focal
-plane in order to accumulate sufficient statistics from the stars in
-the relatively small number of images available at the time.  We have
-found that a single flat-field set can be used for all PS1
-observations to yield photometric systematic errors at the level of \approx
-2\%.  PS1 benefits in this regard from the stability of having a
-single instrument which is rarely removed.
+This correction was made on a relatively coarse \newtext{(\approx 1200
+  CCD pixels per sample)} grid across the focal plane in order to
+accumulate sufficient statistics from the stars in the relatively
+small number of images available at the time.  We have found that a
+single flat-field set can be used for all PS1 observations to yield
+photometric systematic errors at the level of \approx 2\%.  PS1
+benefits in this regard from the stability of having a single
+instrument which is rarely removed.
 
 Photometry of the PS1 images is performed using a
@@ -346,5 +349,10 @@
 photometry, resulting in photometric systematic uncertainties in the
 range 7 - 12 millimagnitudes, depending on the filter
-\citep{2013ApJS..205...20M}.
+\citep{2013ApJS..205...20M}.  \newtext{We note that the PV3 analysis
+  used for the public release includes a flat-field correction
+  measured with a much finer spatial sampling than the PV2 analysis,
+  with 40 CCD pixels per superpixel.  As a result, some of the
+  fine-grained structure discussed below is corrected in the public
+  release (see however the caveats in the discussion section below).}
 
 For all objects, positions are measured from the PSF model for the
@@ -393,10 +401,11 @@
 the boule from which they came.  This gives the impression that a
 similar mechanism is responsible for the pattern observed in the PS1
-photometry and the DECam photometry, namely the diffusive effects of
-lateral electric field variations in the detectors.  In the next
-section, we will make the case that the patterns observed in the PS1
-photometry residuals are {\em not} caused by this mechanism, but are
-instead caused by variations in the {\em vertical} electric field (the
-field direction perpendicular to the CCD surface).
+photometry and the DECam photometry, namely the \oldtext{diffusive
+  effects of} \newtext{migration of charge by} lateral electric
+\newtext{fields} \oldtext{field variations} in the detectors.  In the
+next section, we will make the case that the patterns observed in the
+PS1 photometry residuals are {\em not} caused by this mechanism, but
+are instead caused by variations in the {\em vertical} electric field
+(the field direction perpendicular to the CCD surface).
 
 First, in this section, we will describe how we have measured the