diff --git a/src/graphs.js b/src/graphs.js
index fc48a70e0..2ec88855d 100644
--- a/src/graphs.js
+++ b/src/graphs.js
@@ -35,6 +35,7 @@ async function getContainerStats(name, fromMinutes, noNullPoints) {
     const timeBucketSize = fromMinutes > (24 * 60) ? (6*60) : 5;
     const graphiteUrl = await getGraphiteUrl();
 
+    // https://collectd.org/wiki/index.php/Data_source . the gauge is point in time value. counter is the change of value
     const targets = [
         `summarize(collectd.localhost.docker-stats-${name}.gauge-cpu-perc, "${timeBucketSize}min", "avg")`,
         `summarize(collectd.localhost.docker-stats-${name}.gauge-mem-used, "${timeBucketSize}min", "avg")`,