in v$sesison table there are two columns

logon_time - date
last_call_et number

i am not getting what is the meaning of the column last_call_et , is this in minutes, seconds ?

SQL > select login_time , et_number from v$session.

--------- ------------
19-NOV-04 216
19-NOV-04 223
19-NOV-04 3752
19-NOV-04 3752
19-NOV-04 3753
19-NOV-04 3753
19-NOV-04 1518
19-NOV-04 1540
19-NOV-04 14138
19-NOV-04 2945
19-NOV-04 1518