As concerns the pulley, since it consists of a thin ring connected to the axis by means of very thin spokes, its mass can be considered uniformly distributed over the circumference.
Given this arrangement, in calculating the value of the acceleration it is sufficient to include the pulley in the total mass of the bodies in movement.
In any case, the influence of the pulley and the supporting wheels can be taken into account with good approximation by adding, in calculating the acceleration, a constant of the total mass of the bodies suspended on the string. Once the value of this constant has been determined in a preliminary experiment, the acceleration of gravity can be measured with good precision.