The following Splunk query will display successful windows logins and overlay an average on visualizations.
source="WinEventLog:Security" (Logon_Type=2 OR Logon_Type=7 OR Logon_Type=10) (EventCode=528 OR EventCode=540 OR EventCode=4624) | timechart count(EventCode) as count | eventstats avg(count) as Average | eval average=round(average,0) | rename count as "Successful Logons"