diff --git a/ampel-firmware/web_server.cpp b/ampel-firmware/web_server.cpp
index cb48ff88fb80613d91fe389547d2140e48e2bc17..a0c37bcf2daf248dc40c29796420acdea0d66b6c 100644
--- a/ampel-firmware/web_server.cpp
+++ b/ampel-firmware/web_server.cpp
@@ -141,7 +141,7 @@ namespace web_server {
         ".then(_=>Plotly.newPlot('graph',data,layout,{displaylogo:false}))"
         ".catch(console.error);"
         "xs=[];y1=[];y2=[];y3=[];"
-        "d={x:xs,type:'scatter',mode:'lines+markers',marker:{symbol:123}};" // diamond-tall-open from https://plotly.com/python/marker-style/
+        "d={x:xs,type:'scatter',mode:'lines+markers',marker:{size:3}};" // circle marker (symbol 0), from https://plotly.com/python/marker-style/
         "data=["
         "{...d,...{y:y1,name:'CO<sub>2</sub>',line:{color:'#2ca02c'}}},"
         "{...d,...{y:y2,name:'Temperature',yaxis:'y2',line:{color:'#ff7f0e',dash:'dot'}}},"