Is there truly an accurate way to measure the sea level of a location?

The technology for altimeters has changed over time. Some use pressure measurements and others use satellites (GPS technology) or radar to determine the altitude of a given place (you can use sea level as the base against which you are measuring as in your example). Properly calibrated equipment (particularly pressure measures) can be pretty accurate. GPS accuracy depends on a lot of variables (number of satellites hooked in, satellite position relative to the horizon, etc.). I haven’t ever measured Denver, so I can’t speak to the accuracy of the mile-high claim. I imagine pilots that fly over the Rocky’s have a pretty accurate sense of just how high Denver is so one might be able to shed some light . . .

The problem is with measuring sea level is that the sea isn’t actually level. For instance, mean sea level at the Pacific end of the Panama Canal stands 8 inches higher than at the Atlantic end.

The concept of sea level is a statistical average. Tides at any given shore point vary widely. This variation is due largely to the gravitational forces of the moon, pulling (sloshing) the mass of water around on earth. Sea level is the historical mid-point of the high and low tide at that point. With GPS measurements, the altitude above sea level, at Denver or any other location, is accurate within a few millimeters.

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