sql difference rounds

Why is my difference rounded:

'Checking space left in data_ts:'

          TOTAL_BYTES

       18,880,659,456

           USED_BYTES

       17,796,554,752

 Space
Left

        1,000,000,000

Here's my script:

set heading on verify off
col total_bytes format 999,999,999,999,999 new_value tbytes

col tbytes format 999,999,999,999,999
col used_bytes format 999,999,999,999,999 new_value ubytes
col ubytes format 999,999,999,999,999
col space_left format 999,999,999,999,999 head 'Space Left'

spool space_left
prompt
prompt 'Checking space left in &1:'
prompt
select sum(t.bytes) total_bytes
from dba_data_files t
where t.tablespace_name = upper('&&1')
/

select sum(u.bytes) used_bytes
from dba_extents u
where u.tablespace_name = upper('&&1')
/

select (&&tbytes) - (&&ubytes) space_left from dual
/

Thanks,

Debi

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Author: Debi
  INET: dlorraine_at_ucdavis.edu

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