A funny example of this in practice happened a few years ago during the United Airlines and Continental Airlines merger. When they switched computer systems, s

A funny example of this in practice happened a few years ago during the United Airlines and Continental Airlines merger. When they switched computer systems, somehow they switched the method they used to calculate the distances between cities for their frequent flyer program. Before the merger, both companies used the ellipsoid method. During the computer systems cutover, the method suddenly changed to a spherical approximation. They also used an incorrect The difference resulted in shorting flyers of a few (I think the most I saw was 40) frequent flyer miles per leg. They got caught within a couple days and 'fixed' the 'accidental' change. One of those things they seemed to hope no individual would catch but that over many many flyers would add up to a significant cost savings.