This paper deals mainly with methodical aspects of particle size determinations, viz. principal idéas and design of differential and bidifferential sedimentation balances. The differential balance operates with two sedimentation pans at slightly different heights in the suspension. The difference in load on the pans is simply related to the cumulated curve. The second one operates with three pans under the same condition and is actually a condensed form of a four pan arrangement and it gives directly the size-frequency distribution. The deviation of the balance is at present electro-magnetically compensated by hand since a proper recorder is not yet available or constructed. By a special device “the inherent error” in mechanical analysis is eliminated. Some results are discussed with respect to other methods and to the stability of the sol. — The construction is further improved.