They do that in order to be able to get a figure off the base circle without being too concerned with the various take up ramp designs... There isn't really any difference in using the .050 numbers, but you have to make sure whatever you're basing the final decision on is based off that same set of numbers because the dynamic ratio you calculate will be much different than one based on "base circle" calculations. I always use the KB site, so my experience is based on those figures.
