A Device known as the Simplified Astro Platten (S.A.P.) is presently being marketed by the Bucks. Gear and Engineering Co. Ltd., of Middle Lane, Mount Pleasant, Aylesbury. It consists of a large rectangular plastic sheet some 29 in. by 16 in. on which are engraved two graduated semicircles with parallel diameters separated by a space of 2 inches. This sheet, on which pencil lines may be drawn and which can easily be cleaned when the lines are no longer required, is housed in a stiff plastic protective envelope. A mimeographed booklet of instructions includes examples and answers, for practice. There is no indication of the principles on which the device is based but the idea is certainly not new.