Hi,
I'm sorry for late reply.
When the internet connection is lost, this gauge is not updated with new data, but the 'RealtimeUpdateComplete' event is triggered.
You can test even with this demo data (http://www.fusioncharts.com/demos/gallery/chart_barebone.asp?angular_14)
Just run this command: FusionCharts.items["sampleChart"].addEventListener("RealtimeUpdateComplete", function(){console.log('a')})