Thanks for the comment. I have developed it completely by myself. Node-RED (especially when using the node-red-dashboard node) is really an excellent tool for doing these things.
I also must say that I am very happy with the accuracy of the emonTx sensor node. In the example below you see that as expected the measured “switch on” power should correspond with the measured power decrement when switching off the device. But that the “switch on” average (= 19.33 watt) would be so close to the switch off decrement average (= -19.00 watt) is really amazing.