Current guidance from Devices WG appears to be to use an Observation with subject= [the Patient], and device=[the Device] (or DeviceMetric) to record a device setting (or measurement) during a procedure.

If we are recommending that .device be used to identify the device in the case where a patient is involved, how do we identify the device when the patient is not involved (is subject empty)? What is the use case where the device is the subject of the observation (and if so, is device empty)? It would be odd to search for the device in .subject some of the time, and in .device other times (although actually, we already may have to search in the observation or in the referenced DeviceMetric).

Additional use cases to consider are calibration of the device outside a patient context, and observations about the device ("the stove was hot"), which are neither measurements nor settings of or about the device.

Are there cases where the device is the focus of the observation?

Please clarify (and ensure consistency between) the use cases for use of Device in each of the Observation elements.

(I dislike that there is no single place to look for Observations involving a device. It looks like I'd need to query all of subject, focus, and device, and even then I wouldn't get devices that are only referenced by metric.)