Obviously, your go-to source for the accurate time was, and remains, Big Ben — even if you can’t see it, you can HEAR it, right?

But what if you wanted to be as accurate as possible? Obviously, if you’re far from Ben, you’d hear the chimes later than someone quite close to it — with the speed of sound being about 1,126 feet per second, it matters.

Fortunately, there’s a map you can consult, with concentric rings showing the delay from “true” time.

Neat.