Originally posted by AJW_ID01
Then, of course, I became confused as to why:

BLOCKS (which I believed would be those below HWM) and
EMPTY_BLOCKS (which I believed would be those above HWM)

did not seemingly add up to the total within blocks from all extents.
If you add BLOCKS and AMPTY_BLOCKS from DBA_TABLES and compare this to blocks in DBA_SEGMENTS, what is the difference? AFAIK, the difference between those two numbers shopuld be 1 block (which, if I'm not mistaken, is the segment header block, which is not counted neither in BLOCKS nor in EMPTY_BLOCKS).

So, yes, BLOCKS shows the number of blocks below (and including the one with) HWM, while EMPTY_BLOCKS shows the number of blocks above HWM. The sum of those two numbers should be equal to BLOCKS.DBA_SEGMENTS-1.