The calculator seems a tad inaccurate for required speed of a circular orbit (In the realm of decimeters per second), since the speed it gives results in an orbit that is off by a couple of km. (Ex: The speed it gives as a requirement of an orbit that is around 2871003 meters from Kerbin is somewhere around 1008.5 m/s, when it seems to be actually at around 1008.67 m/s)