David is right but how do you know that it subtracted that many seconds?

Code:
appdev@NICK>select (sysdate - 3/86400) "Secs?"
  2  from dual
  3  /

Secs?
---------
08-OCT-02
You can see that it will have to be tried this way......

Code:
appdev@NICK>select (sysdate+1/(1*60*60*24)-sysdate-2/(1*60*60*24))*(60*60*24) "Secs!"
  2  from dual;

     Secs!
----------
        -1
Cheers!