Irlandes, before I disappear up my own backside with this, your original post pointed out that at 1300 lbs AUM in ISA conditions your hover ceiling would be 8500 DA. Then you compared an increase in OAT (worsening conditions for the engine with the throttle wide open) between what common sense told you (7300' DA) and what the graph told you (8000'DA). The performance graph allows you to operate only 500' (not a great deal)below your ISA state when the OAT has increased by 10 deg(quite a lot). I am afraid I just cannot believe dropping 500' in PA compensates for an increase in OAT of 10 degrees, even in a crappy old piston engine - I am just going to have to go into the loft and find all my old piston notes ad there must be formula for this somewhere.