{ "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": { "lower": 0, "upper": 66.667 }, "zones": [{ "lower": 60.0, "state": "alarm", "message": "Engine exceeds maximum rpm!" }] } } } } }