The Banner explains why the marker on Eutaw Street for Gunnar's 462-foot HR from yesterday doesn't quite reach the one for Jim Thome's 440-footer in 1996. It's because they started using Statcast distances in 2015, and it measures things differently.
The estimated distance from Statcast is the most accurate measurement available, but it doesn’t mean the ball literally landed 462 feet away from home plate. Statcast measures where the ball would have landed on a flat ground, if there was no impediment on the way back to the playing surface. When Oriole Park at Camden Yards was built 31 years ago, the playing field was excavated into the ground. The right field wall rises about 21 feet — Eutaw Street, then, is a story above the playing field.
Before Statcast, Orioles team historian Bill Stetka said “there was just a chart that had a graphic line all the way across every dimension of the outfield,” which allowed for an estimated distance to be called on where it landed. That’s how Thome received a 440-foot measurement. And it’s how Ken Griffey Jr., who struck the warehouse on the fly during the 1993 home run derby, has a plaque that says 465 feet. With Statcast, both distances would be estimated longer.
Gunnar Henderson’s 462-foot homer and the confusion of Eutaw Street markers at Oriole Park - The Baltimore Banner