A number of researches have highlighted inconsistencies within the first book of On the Equilibrium of Planes.[1][17] Berggren questions the validity of much of book one, noting for instance the redundancy of Propositions 1-3 and 11-12. However, he follows Dijksterhuis in rejecting Mach's criticism of Proposition 6 and highlighting instead its significance, namely "if a system of weights suspended on a balance beam is in equilibrium when supported at a particular point, then any redistribution of these weights, that preserves their common centre of gravity, also preserves the equilibrium."[2][3]