Well, BSP, I applaud your desire to raise the issue, though I'm appalled that it's considered necessary. How do most PPLs think their aircraft get airborne - little 'lift fairies'
It also raises the point, that if you are aware that calculations need to be made, and graphs consulted, you need to be able to do it accurately. Looking at my and FFB's posts you can see quite clearly that it couldn't have been 4000 ft DA- possibly 3000 ft if it was the 39 C day we had a few years ago. That's obviously an error on the safe side, but the reverse would be rather less desirable.