diff --git a/powerwall.sh b/powerwall.sh
index bd4bb602..fccc60fe 100755
--- a/powerwall.sh
+++ b/powerwall.sh
@@ -613,7 +613,7 @@ TEST(){
 	temptotal=0
 	while IFS=$'\t' read date sensorid temp hum ;do
 		# echo date:$date sensorid:$sensorid temp:$temp hum:$hum
-		temptotal=$(expr ${temptotal} + ${temp})
+		temptotal=$((${temptotal} + ${temp}))
 		echo "- ${temptotal} + ${temp}"
 	done  < <(${mysql_conn} -se "USE servermonitor; SELECT date,sensorid,temp,hum from sensor_data WHERE sensorid=2 ORDER BY id DESC LIMIT 10;")