missing page when calculating extents

Apologies if this is old hat ... I have been trying to calculate extent sizes, I faithfully followed what it said in chapter 10 of the Tutorial, but I found an interesting 'problem' take for example a table with a rowsize of 12 bytes and no indexes the number of rows per page should work out as (pagesize-28)/(rowsize+4) = (2048-28)/(12+4) = 2020/16 = 126 I should therefore be able to fit 4*126 = 504 rows in 4 pages (one 8K extent) However, I can only fit 3*126 = 378 rows in 4 pages; when I insert the 379th row I get a second extent. The same applies to other extent/row sizes, there is always one "missing" page. Is this because OnLine always wants at least one empty page or is it because the "missing" page has some other info on it? And what about Indexes, the calculations in chapter 10 seem way out. When I added a 4 byte index to my table, I could only fit 669 rows into 12 pages any clues anyone?? [machine = HP-UX A.09.04 E 9000/847, OnLine = 5.02.UC6] -- John Cooke AT&T Network Systems UK Though the opinions are mine, they remain the intellectual property my employer