diff --git a/NOTES.md b/NOTES.md
index d8ee5a7..4f482df 100644
--- a/NOTES.md
+++ b/NOTES.md
@@ -27,6 +27,9 @@ https://web.archive.org/web/20200109053708/https://www.highcharts.com/demo/area-
 Running Python code in browser:
 https://github.com/brython-dev/brython
 
+Range series, for showing min/max and avg:
+https://www.highcharts.com/docs/chart-and-series-types/range-series
+
 Graphs
 ------