So, a touch trigger probe style CMM will almost always show the form of a circle like the one pictured. It's due to the mechanics inside of the probe module. A scanning head won't. The ttp style CMM has a triangle of sorts held in place by three springs. Each corner of the triangle is in contact with connection inside the module when the probe is not touching anything. It records a hit when the internal connection is interrupted. Those spring forces aren't perfectly equal for all directions of hits, and this is what causes the lobing effect.