Scientists scanning and mapping the Giza pyramids say they've discovered that the Great Pyramid of Giza, the oldest of the world's Seven Wonders, is a bit lopsided.

And really, just a bit. The pyramid's exact size has stumped experts for centuries, as the "more than 21 acres of hard, white casing stones" that originally covered it were removed long ago.

Reporting in the most recent issue of the newsletter "AERAGRAM," which chronicles the work of the Ancient Egypt Research Associates, engineer Glen Dash says that by using a new measuring approach that involved finding any surviving remnants of the casing in order to determine where the original edge was, his team found the east side of the pyramid to be a maximum of 5.55 inches shorter than the west side.

The question that most intrigues him, however, isn't how the Egyptians who designed and built the pyramid got it wrong 4,500 years ago, but how they got it so close to perfect.

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"We can only speculate as to how the Egyptians could have laid out these lines with such precision using only the tools they had," Dash writes.

He tells Live Science his working hypothesis is that the Egyptians laid out their design on a grid, noting that the great pyramid is oriented only slightly away from the cardinal directions (its north-south axis runs 3 minutes 54 seconds west of due north, while its east-west axis runs 3 minutes 51 seconds north of due east)—an amount that's "tiny, but similar," Atlas Obscura points out.

(A German teen illegally scaled the 455-foot pyramid earlier this year.)

This article originally appeared on Newser: One of World's Seven Wonders Stands a Bit Askew