You can open any number of Student Data Base screens with one SecurID, as long as you use a different PRN (pseudo-random number, from the SecurID) for each screen. For example, you might want to look at a student's schedule with one SDB screen while looking up courses on another SDB screen. If you have two screens open, you won't have to keep typing in the student number to get back to the student's schedule.
You can also use one SecurID to set up the Student Data Base on more than one computer, although this should not be done on a regular basis. Anyone regularly using the SDB should have their own usercode.