diff --git a/run-time.sh b/run-time.sh
index d23352c..5708fff 100755
--- a/run-time.sh
+++ b/run-time.sh
@@ -1,9 +1,14 @@
 #!/bin/bash
+if [ "$#" -ne 1 ]; then
+	echo "Bad usage of run-time.sh"
+	echo "./run-time <number of runs>"
+	exit 1
+fi
+echo "Starting $1 runs of surfaces-unies"
 start=$(date +%s.%N)
-nbloops=10
-for i in `seq 1 $nbloops`; do
+for i in `seq 1 $1`; do
 	./bin/surfaces-unies -c -i ./img/asterix.ppm
 done
 end=$(date +%s.%N)    
-runtime=$(python -c "print((${end} - ${start}) / ${nbloops})")
+runtime=$(python -c "print((${end} - ${start}) / ${1})")
 echo "Average runtime was $runtime"