Index: /trunk/doc/psphot/psphot.tex
===================================================================
--- /trunk/doc/psphot/psphot.tex	(revision 11598)
+++ /trunk/doc/psphot/psphot.tex	(revision 11599)
@@ -191,5 +191,8 @@
   level must be reached for images with 250 mas pixels, implying
   PSPhot must introduce measurement errors less than 1/50th of a
-  pixel.
+  pixel. \note{the choice of F32 parameters places a numerical limit
+  of 1e-7 on the accuracy of a pixel relative to the size of a chip
+  (since a single data value is used for X or Y).  For the $4800^2$
+  GPC chips, this yields a limit of about 0.25 milliarcsecond.}
 
 \item {\bf processing time of 45 seconds} This requirement depends