diff --git a/README.md b/README.md
index 7c8edea..7df4106 100644
--- a/README.md
+++ b/README.md
@@ -63,6 +63,8 @@ sudo apt install php7.0 php7.0-curl php7.0-gd php7.0-intl php7.0-mbstring php7.0
 
 [cJSON](https://github.com/DaveGamble/cJSON)
 
+[g/m³ formula](http://www.wetterochs.de/wetter/feuchte.html)
+
 Laravel
 
 [Laravel Charts](https://erik.cat/projects/Charts/docs/5)