diff --git a/README.md b/README.md
index 3f2146a..edb1723 100644
--- a/README.md
+++ b/README.md
@@ -2,9 +2,15 @@
 
 Icinga2/Nagios check program for Raspberry Pi temperature
 
+## Requirements
+
+- `bc` for floating point calculation
+- Adding executing user to video group: `sudo adduser nagios video`
+
 ## Arguments
 
 - `--warning 50`: Temperature above which the result is warning
 - `--critical 70`: Temperature above which the result is critical
 - `--fahrenheit`: All temperatures in Fahrenheit (°F)
 
+
diff --git a/check_rpi_temp.sh b/check_rpi_temperature.sh
similarity index 87%
rename from check_rpi_temp.sh
rename to check_rpi_temperature.sh
index 18c9b7e..d30df3f 100755
--- a/check_rpi_temp.sh
+++ b/check_rpi_temperature.sh
@@ -4,6 +4,12 @@
 
 echoerr() { echo "$@" 1>&2; }
 
+if ! $(command -v bc); then
+	echoerr Please install bc
+	exit -2
+fi
+
+
 WARN=50
 CRIT=70
 FAHRENHEIT=false
@@ -12,14 +18,14 @@ while [[ $# -gt 0 ]]; do
 	case $1 in
 		-w|--warn|--warning)
 			case "$2" in
-				''|*[!0-9]*) echoerr "Argument for \"$1\" has to be a number";;
+				''|*[!0-9]*) echoerr "Value for \"$1\" has to be a number"; exit -3;;
 			esac
 			WARN=$2
 			shift; shift
 			;;
 		-c|--crit|--critical)
 			case "$2" in
-				''|*[!0-9]*) echoerr "Argument for \"$1\" has to be a number";;
+				''|*[!0-9]*) echoerr "Value for \"$1\" has to be a number"; exit -3;;
 			esac
 			CRIT=$2
 			shift; shift
@@ -45,7 +51,7 @@ done
 
 if [ $CRIT -le $WARN ]; then
 	echoerr "Critical threshold ($CRIT) has to be greater than Warning threshold ($WARN)"
-	exit 1
+	exit -3
 fi