Actually, ideally I'd like to have two columns (both as %) showing the % of distinct events and the % of all events. That way I can see both what device our visitors are using and if one device is causing more traffic.
I can do that from here (if i could just divide by total)
eventtype=pageactions tag=external_traffic session_id=*
| fillnull value=blank devicetype
| stats dc(session_id) as unique_sessions, count as event_counts by devicetype
| table devicetype unique_sessions event_counts
| addtotals row=f col=t labelfield=devicetype label=total