diff --git a/g14control.sh b/g14control.sh
index 10787a7..d88d347 100755
--- a/g14control.sh
+++ b/g14control.sh
@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
+set -x
+
 # g14control.sh
 #
 # version: 1.0
@@ -27,14 +29,16 @@ disp() {
 	STEP=$((MAX/10))
 	CURRLEVEL=$(cat ${INTERFACE})
 
-	[[ ${1} =~ ^[0-9]{1,${#MAX}}$ && ! ${1} > ${MAX} ]] && \
+	if [[ ${1} =~ ^[0-9]{1,${#MAX}}$ && ! ${1} > ${MAX} ]]; then
 		LEVEL=${1}
-	[[ ${1} == "up" && ${CURRLEVEL} < ${MAX} ]] && \
-		LEVEL=$((CURRLEVEL+STEP))
-	[[ ${1} == "down" && ${CURRLEVEL} > 0 ]] && \
-		LEVEL=$((CURRLEVEL-STEP))
+	elif [[ ${1} == "up" && ${CURRLEVEL} < ${MAX} ]]; then
+		[[ $((CURRLEVEL+STEP)) > ${MAX} ]] && \
+			LEVEL=${MAX} || LEVEL=$((CURRLEVEL+STEP))
+	else [[ ${1} == "down" && ${CURRLEVEL} > 0 ]]
+		[[ $((CURRLEVEL-STEP)) < 0 ]] && \
+			LEVEL=0 || LEVEL=$((CURRLEVEL-STEP))
+	fi
 
-	echo ${LEVEL}
 	echo ${LEVEL} > ${INTERFACE}
 
 	CHKLEVEL=$(cat ${INTERFACE})