diff --git a/viz/gnuplot/average4v.awk b/viz/gnuplot/average4v.awk
index 439dc31..55d7eaf 100755
--- a/viz/gnuplot/average4v.awk
+++ b/viz/gnuplot/average4v.awk
@@ -2,16 +2,30 @@
 
 BEGIN	{
 	flag_debut = 1;
+	lastminute = 0;
+	cumul      = 0.0;
+	compte     = 0;
 	}
 
+# iterate over all the input lines
 	{
 	if (flag_debut) {
 		debut = $1
 		flag_debut = 0
 		}
-	minutes = ($1-debut) / 60;
-	val = ($2 + $3 + $4 + $5) / 4.0;
-	print minutes, val;
+	minutes = int(($1-debut) / 60);
+	if (minutes == lastminute) {
+		val = ($2 + $3 + $4 + $5);
+		cumul += val;
+		compte += 4;
+		}
+	else	{
+		val = cumul /compte;	
+		print minutes, val;
+		lastminute = minutes;
+		cumul = 0;
+		compte = 0;
+		}
 	}
 
 
diff --git a/viz/gnuplot/plot-one.sh b/viz/gnuplot/plot-one.sh
new file mode 100755
index 0000000..8cb6427
--- /dev/null
+++ b/viz/gnuplot/plot-one.sh
@@ -0,0 +1,20 @@
+#!/bin/bash
+
+INFILE="../../serial/foo.dat"
+NBLINES=2000
+TMPFILE="/tmp/dd2data.$$"
+IMAGE="average4v.png"
+
+tail -${NBLINES} ${INFILE} | ./average4v.awk > ${TMPFILE}
+
+gnuplot << __EOC__
+set term png 	size 800,600
+set output 	"${IMAGE}"
+set grid
+set title	"Average4v"
+set xlabel	"minutes"
+set ylabel 	"température"
+set yrange	[ 5.0 : 30.0]
+plot "${TMPFILE}" with lines
+__EOC__
+