How to calculate time scale difference?

SQL> desc xx_time
Name Type
---------------- -------------------
STANDARD_START NUMBER(4)
STANDARD_STOP NUMBER(4)


SQL> select * from xx_time

STANDARD_START STANDARD_STOP
-------------- -------------
2100 400
1600 2300
1930 230

How to calculate time scale difference?
Means the total hours between 2100 and 400 will 7 Hours.
I want to calculate the hours in between.

It would be far better and easier if you could store your start/stop times as Oracle DATE's - in which case (stop_date - start_date)/24 is the result you want.

If you must store them as numbers, then you're stuck with doing the arithmetic the hard way.