Give me a minute to explain the second. In land surveying, positional accuracy will depend on how carefully you measure a second. If we move along a meridian on the surface of an ellipsoid, advancing from one latitude to another, then the distance moved is called a meridional arc (M). Let’s say that we are doing this in the area around Denver, at about 39.7 degrees North. And let’s set the distance traveled equal to one second of arc of latitude (from 39°42’00” to 39°42’01”). What distance would I have traveled on the ground in meters or feet?
 

First, we calculate the radius of curvature of the ellipsoid in that immediate area. It is given by: