It's normal for people to lose height as they age. The same seems to be true for structures.

The National Park Service and the National Geodetic Survey have announced that the Washington Monument is not quite the 555 feet, 5-1/8 inches tall as measured by government surveyors following its long-delayed completion in 1884. Using 21st Century surveying technology, the agencies have determined that 130 years of weather, lightning hits, and at least one earthquake have whittled 3/8 of an inch from the iconic marble obelisk’s height.

So that makes the Monument 555 feet, 4-3/4 inches tall, right? Yes and no.

Using height certification standards established by the Council on Tall Buildings and Urban ­Habitat (CTBUH), the Monument officially checks in at 554 feet, 7-11/32 inches.

One would think the nation’s first president, himself a surveyor, would be a stickler for accuracy and scoff at the oft-heard assumption that particular figure is “close enough for Government work.” So where did those slivers of size go?

The NPS/NGS survey was conducted during the recently completed project to repair damage stemming from the 5.8 magnitude earthquake in August 2011, the strongest East Coast temblor in more than a century. While other post-quake field surveys indicated that the Monument had not settled or become misaligned, the repair project afforded the opportunity to re-measure the structure using the same brass foundation markers believed to have been the basis for the 1885 survey.

Once the 3/8-inch discrepancy was confirmed, it didn’t take long to figure out why. As the tallest point in downtown DC, the Monument’s 9-inch engraved cast-aluminum tip has taken a lot of lightning strikes over the decades, not to mention the pounding of rain, snow, hail, wind-blown sand, and whatever else Nature has seen fit to dole out (a feeling that George Washington and his successors would know quite well.)

Such intense wear on a such soft metal makes sense, say the agencies. And it offers a chapeau tip to the comparatively high accuracy of the post-completion survey conducted by the Monument’s Director of Construction, Army Lt. Col. Thomas L. Casey.

But something else besides “life” happened during those intervening years. The CTBUH, founded in 1969, determined that a structure’s true height should be measured  from its lowest significant open-air pedestrian entrance.

For the Washington Monument, that point (located at the main entrance) is 8-5/8 inches higher than those ancient brass plates. Had a comparable survey been taken from that location in the past, it too would likely find a differential close or equal to the 3/8-inch height change.

Being “ internationally known as the arbiter of the criteria upon which tall building height is measured,” according to CTBUH’s website, 554 feet, 7-11/32 inches will now be the Monument’s official “architectural height.”

Unless you ask NPS, which plans to keep the “historic height” of 555 feet, 5-1/8 inches currently found in all its brochures and online media.

What would George Washington think? It might well make for an interesting discussion over brandy at Mount Vernon…once you finished explaining what “online media” is.