Consisting of four 18"(45 cm) long wooden blocks each with ten inset knobbed cylinders graded in height and/or diameter. In block No.1 - the cylinder increases in both height and diameter. In block No.2 - Cylinder increases in diameter but remain constant in height. In block No.3 - Cylinder decreases in height but increases in diameter. In block No.4 - Cylinder increases in height while diameter remains constant.