I've memorized a few values, like the radius and mass of the Earth. What meaning would it be for them, I wonder, if I answered '40,000 km / (2 pi)' (or '25,000

I've memorized a few values, like the radius and mass of the Earth. What meaning would it be for them, I wonder, if I answered '40,000 km / (2 pi)' (or '25,000 miles / (2 pi)'? BTW, there are three factors that affect your calculation which you left out. First, the fencepost error. While SF and NYC have two timezones in between, neither city is on the furthest edge of its timezone. With better knowledge, an estimate of 3.5 is more correct, giving (24/3.5)3000/(2 pi) = 3274 miles. Second, 3,000 miles is the driving distance, not the great circle distance, which is only 2,500 miles. (24/3.5)2500/(2 pi) = 2728 miles. Still, I think 3,000 miles is good for the ballpark estimate you made, and it's certainly not a fact I have at hand. Third, those two cities lie at about 40 N latitude, so you computed the length of that latitude, not the length of the equator. You need to divide by cos(40 degrees). cos(45 degrees) is sqrt(2)/2 = 0.707, so I'll use 0.75. (24/3.5)*2500/(2 pi)/0.75 = 3637.