Constituent clarification

I noticed that there was some confusion between two colleagues' queries between the use of time.ss and time.second so I thought I would blog about it briefly.

q)t:09:00:02.000
q)t.ss
2
q)t.second
09:00:02

select count i by time.ss from ... will count the number of records that have identical number of seconds where select count i by time.second from ... will group records by its timestamp ignoring milliseconds.