With all due respect to Johnny, and as Dave partly indicated, Johnny's response to the question about effective mass is incorrect on all counts. The effective mass is a function of the distribution of the mass of the tonearm from pivot to headshell, including the cartridge mass, (not just the total mass per se), which is why you cannot determine effective mass by simply weighing the tonearm, and the counter-weight also contributes to effective mass by a factor related to the square of the distance from the pivot point to the center of mass of the CW times the mass of the CW. Thus, the "subweight" increases effective mass on both counts; it shifts the center of mass of the total CW further away from the pivot and it adds to total mass. Apologies to Johnny...