@BD: I *think* I'm with you. Let's see: The elevation of EGBJ's ARP found in the AIP is its measured, geographic distance above actual, wet & salty, mean sea level. The sea level on which QNH is quoted isn't real in that its pressure of 1013.25hPa only occurs on a spherical earth at 15 degrees C in which UK is still in EU. Therefore, calculating QFE from QNH must consider where EGBJ would actually be if the world was a perfect, slightly lumpy sphere and it was warm outside - neither of which are true. Since this figure is not published in the AIP, I'm on a hiding to nothing.
However, if I want to create a model that gives more similar results to the real world, using the runway elevation instead of the ARP elevation will do the trick for EGBJ - and may or may not work for all the other airfields in UK..
@Beamer: You're right, but it makes me happy and keeps my head warm. In other news, my model for daytime temperatures using a 10 year monthly average min & max temps report and some cosines seems to work quite well. It was worth going to school after all.
@LookingForAJob: Thank you for that. The altimeters in the aircraft I fly give generalisations at best; Combined with my ham-fistedness, plus/minus a couple of hPa will make no difference at all to my circuit flying. Nice to know the tower is well-equipped though.
