{
  "uuid": "urn:mrn:signalk:uuid:c0d79334-4e25-4245-8892-54e8ccc8021d",
  "propulsion": {
    "instance0": {
      "label": "Main Engine",
      "revolutions": {
        "value":  43.5,
        "timestamp": "2014-08-15T19:00:15.402Z",
        "$source": "foo.bar",
        "meta": {
          "description": "Engine revolutions (x60 for RPM)",
          "units": "Hz",
          "displayName": "Tachometer",
          "shortName": "RPM",
          "displayScale": {
            "upper": 66.6667
          },
          "zones": [{
            "lower": 60.0,
            "state": "alarm",
            "message": "Engine exceeds maximum rpm!"
          }]
        }
      }
    }
  }
}