Measuring the difference of a value - looking for a best practice

---

Hello community, I like to measure the difference of a value given from a device via MQTT.

So far I setup a MQTTSensor giving the actual value each 5 minutes.
This is working fine, now I like to:

1. measure the gap since the last measurement
2. trace the measured gap

I tried a couple of things but this were quiet complex. So I guess there might be a better way doing this.

Can anyone give me an idea about the best practice doing this?

Greetings Patrick

Hi @cyberpaul0815, one of the variants:

variable:

    {
      "name": "trace_gap",
      "value": 0
    }

variable device:

    {
      "variables": [
        {
          "name": "trace_gap",
          "expression": "($trace_gap)",
          "type": "number",
          "discrete": true
        }
      ],
      "xAttributeOptions": [],
      "id": "gap-var-dev",
      "name": "Gap var dev",
      "class": "VariablesDevice"
    }

rule:

    {
      "id": "trace-gap",
      "name": "Trace Gap",
      "rule": "when $location.lat gets updated then set $trace_gap to 1 and after 100 ms set $trace_gap to 0",
      "active": true,
      "logging": true
    }

You can also connect to the Timer device (stop, start, reset). I do I measure this way consumption of heating in the aquarium.

maybe you can use a self created variable with “expression” (instead of value) at the variables menu.
there you can calculate such as below shown for example

then go for the variables device to show the result on the gui.
maybe this helps ?

Thank you!

@cyberpaul0815
if i may ask - how did you solve it (if already done)?