1930.]. Boxed set of nine painted and glazed red wooden apples, each mounted on a metal ‘core’ attached to a flange with hinges to allow for various fractions to be ‘removed’; some light signs of use, with some of the fractions moving more easily than others suggesting increased use, some light rusting to some of the flanges, but overall very good; housed within the original hinged blue cardboard box, 21 x 20 x 6cm, with nine internal compartments, which show some signs of wear and soiling but remain firm, title and instruction label mounted on inside lid, outer box lightly rubbed and worn along joints and corners, based somewhat abraded; overall a lovely set. A scarce and most appealing interactive teaching aid introducing fractions through the use of nine painted and glazed red wooden apples, each mounted on a metal ‘core’ attached to a flange with hinges to allow for various segments or fractions to be revealed (halves, thirds, quarters etc). The present set has been produced by the Dutch firm Critas based in Doorn, and we believe dates to the 1930s. Similar sets were produced in Germany at the same time, notably the ‘Archimedes’ fraction calculator, which was patented by Hugo Jung in Stuttgart in 1927 and produced by Rudolf Lobelenz. Simpler sets consisting of only four apples - one whole, one halved, one divided into thirds, and one quartered, were also produced in both France and Germany.
Such visual and tactile teaching aids allowed students to visualise the concepts under discussion and aid understanding.