I wrote something a few weeks ago about measuring the height of Mount Everest. Now you simply use GPS? The article says that its more complicated than that.

Initially, it was the Trigonometric Survey of India in which they marched across the sub-continent, measuring angles angles and finding distance until being able to measure the height of Mount Everest. George Everest, a surveyor, was an important part of the efforts to measure it. 

Some interesting facts that it came out:

• There was a recent earthquake that lowered its height, but it was only by one inch.
• A legend states that the measurement came out to be exactly 29,000 feet. They figured people would suspect a figure like that, so they tacked on a couple more feet so they published the height as 29,000 feet.
• For GPS you need a receiver. There is one near the top. The official height is from a survey done in the fifties.

There are complications I wasn't aware of. The elevation is the height above sea level. But what exactly is sea level. To begin with, the earth isn't completely round. Sea level is not level due to the tides. It is basically the average of the high and low tides, but that gets a little tricky to measure. That can also differ because other mountains in the area can alter the gravity, which then alters the tide height.

As the article stated, "All of our elevations have an error."