A solid cylinder with ring and a close-fitting bucket of equal volume suffer an apparent weight loss when submerged in water due to buoyancy. When taken apart and immersed again with the cylinder hooked on the bucket, an amount of water equivalent to the weight of the cylinder fills the bucket and can be weighed. Bucket is 5.5 cm x 2 cm. Cylinder is 4.5 cm x 1.5 cm. Includes instructions and dacron line. You need 611-0005 spring scale.