diff --git a/dsv/README b/dsv/README
new file mode 100644
index 0000000..1434472
--- /dev/null
+++ b/dsv/README
@@ -0,0 +1,24 @@
+Setting the PDF viewer
+----------------------
+
+If the environment variable DSV_VIEWER is set, dsv will launch the
+program specified there.
+
+If DSV_VIEWER is not set but DSV_PDFVIEWER is set, dsv will launch
+the program specified in DSV_PDFVIEWER.
+
+If neither DSV_VIEWER nor DSV_PDFVIEWER are set, dsv will run
+xdg-open to launch the viewer.
+
+xdg-open typically defaults to the "evince" viewer. The default
+can be changed from the command line with
+
+xdg-mime default APPLICATION application/pdf
+
+where APPLICATION is one of the *.desktop files typically found
+in /usr/share/applications/ or /usr/local/share/applications/
+
+For example, to make xpdf the default xdg-open (and hence many
+other applications) uses, one would run
+
+xdg-mime default xpdf.desktop application/pdf
diff --git a/dsv/dsv b/dsv/dsv
index 3fdeb9f..7f6a103 100755
--- a/dsv/dsv
+++ b/dsv/dsv
@@ -2,8 +2,8 @@
 #
 # dsv - Improved data sheet viewer
 #
-# Written 2010, 2011 by Werner Almesberger
-# Copyright 2010, 2011 Werner Almesberger
+# Written 2010-2012 by Werner Almesberger
+# Copyright 2010-2012 Werner Almesberger
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -67,8 +67,12 @@ flush()
 		# @@@ should handle error
 	else
 		url=${url%`echo x"$inside" | sed 's/./?/g'`}
-		wget -nv -O "$DSV_DIR/_tmp" "$url"
-		unzip -p "$DSV_DIR/_tmp" "$inside" >"$DSV_DIR/$ds" ||
+		zip=$nm-`basename "$url"`
+		if [ ! -r "$DSV_DIR/$zip" ]; then
+			wget -nv -O "$DSV_DIR/$zip" "$url"
+			# @@@ should handle error
+		fi
+		unzip -p "$DSV_DIR/$zip" "$inside" >"$DSV_DIR/$ds" ||
 		    { rm -f "$DSV_DIR/$ds"; exit 1; }
 	fi
     fi
@@ -161,7 +165,7 @@ search()
 		if $path; then
 		    echo "`pwd`/$DSV_DIR/$file"
 		else
-		    ${DSV_PDFVIEWER:-xpdf} "$DSV_DIR/$file"
+		    ${DSV_VIEWER:-${DSV_PDFVIEWER:-xdg-open}} "$DSV_DIR/$file"
 		fi
 		exit
 	    fi