> Heh. You know, Dave, my husband was once a geologist in another lifetime: he got kind of snooty over your use of the term "tallest" to really mean "highest". No, I don't know what the difference is. He also muttered something about only a geologist would ever want to measure mountain height from the center of the earth, or from the bottom of the ocean floor.

Hehehe. Here's some more pestering info for your husband, though from what you say above, chances are he probably already knows it.
Navigational GPS, when used with info from four satellites instead of the standard three, gives you not only your latitude and longitude, but your altitude. Well and good. But how it does this always makes my mind boggle.
Basically it locates your height (or whatever) on the Earth's surface in relation to where the surface of the Earth *would* be if it was a perfect sphere. But because it's flattened a bit in one direction and bulges a bit in others, and has all those wonderful up-and-down bits that give us Scenery, it's sort of telling you where you are standing in relation to a surface that doesn't exist except as a mathematical concept.
Nobody else I know has a problem with this, maybe I'm just weird. It always gives me the creeps when I really start thinking about it.

Brunnen-"and it's wrong anyway, because the US military scrambles the signals"G