Jammedstab,
Yes, it made me slightly high but as you say it's conservative and no safety issue. I should have twigged when the ATIS had Fata Morgana on it.
And I'm pretty sure the basic formulae work on a standard lapse rate.
There's a more complex one that even takes into account the variation of 'g' with altitude, but you won't be doing that in your head!
I can't type out the formula on the screen so I'll see if I can find a copy online.
Last edited by compressor stall; 25th Oct 2013 at 22:24.