Dan, can we be sure that the Altimeter actually registered with Doug M ? He was, after all, directional rather than vertically involved. Mind you, an electric orange and who knows ?
Worry not, I was an aircraft trade, and also flew as SLF (occasionally) maybe mostly. Never be afraid to ask a question on this thread, most will always respond with a knowledgeable reply, I'm sorry for my flippancy.
I can confirm that the altimeter does register negative figures. A beat up of a sub at Diego Garcia involved a call from the ATC local confirming that our Mode C was giving a -10 ft readout. I will say no more, I've already been bollocked for that story !!!!!!!!
Smudge