PURPOSE: To obtain the proportional distribution of weights by a simple constitution quickly and readily, by attaching an opaque percentage selecting member having a curve edge in an imaginary curve shape and a straight index member on a scale member so that they are freely rotated.

CONSTITUTION: A percent scale 11 is attached on an imaginary curve 9 connecting one point on a periphery and the center of a circle, and a scale table 6 is constituted in a circular shape. Thus a scale member 31 is obtained. A position, which agrees with the center of a circle 3 of the scale member 31 is made to be the center of rotation of an opaque percentage selecting member 32. The member 32 has a curve edge 40, with an imaginary curve 30 having a base point at a point 29 as a model. A 0% scale index 45 indicates the point of the 0% scale of said curve edge 40. The index 45 is provided as a protruded part on the extended line from a straight line connecting the center of the circle 3 and the point 29 at 180°. In alignment with the center of rotation of the percent selecting member 32, an index member 33 comprising a straight rod is provided. Thus, the proportional distribution of the weights of two bodies can be obtained quickly and readily by a simple constitution.