http://www.kb-silvolite.com/kb_car/performance.php?action=details&P_id=15

means you subtract 1.2 cc to total of gasket and head CC.
this is before any machining to give proper quench

say you mill nothing if you have 72 cc head and 8 cc for a composition gasket 72 + 8 - 1.2 = 78.8 compression chamber volume so 9.7 to 1.

Only real way to tell is down fill a cylinder and actually cc heads.