Perhaps not the exact measurements, per se. However, I have noticed the difference between a 3-star and a 2-star restaurant really has to do with the ambiance and the "experience". The food, to be honest, is not that much different, I don't think. In fact, there are many 1-star restaurants which have food that is actually better than some 3-star restaurants.

However, one thing I have noticed in the limited number of 3-star restaurants that I have been to: they all have great ambiance. White linen, multiple utensils, large number of waitstaff, fresh flowers, opulent decor and chandeliers, etc. I think the 3-star cut off is really the whole "feel" and dining "experience" which sets it apart from a 2-star.