diff --git a/Makefile.p690 b/Makefile.p690
index 1bb5ae69aaef8663725827fffc341f108f37688b..3f08eb638e63250dac405bbb4bec9e9df702538d 100644
--- a/Makefile.p690
+++ b/Makefile.p690
@@ -34,6 +34,16 @@ FLG64=-b64
 
 # Define FORTRAN compiler flags.......................
 #
+# On one p690 run, we have these two results: 
+#           Temperature calculations    4243.5252    426.0988      0.0117
+#           Temperature calculations     336.4992     32.3458      0.0077
+# The difference being 
+#  1. number of processors: 4 and 16
+#  2. the compile flags: debug and speed
+# Also, the first run quit sooner; i.e. at a different place
+# The first run stopped on a floating point overflow
+# The second run stopped on a seg fault.
+#
 # -qsave is the default for Fortran77, -qnosave for Fortran90
 # take -qextchk out for the final compile
 # Need -qhalt=s, else the compiler stops on the multiple errors from MPI calls.