The problem: construct the the exact length OT of circular arc OC, see Fig. 2. This construction is one of the traditional geometric problems. The solution is impossible by euclidian construction methods (apply only compass and straight slider). In this worksheet is demonstrated the exact rectification procedure of the problem width applying the cochleoidal curve and the geometric package of Maple. The principle of construction is explained by Hungarian mathematician Paul Sipos (1759-1816) in "Beschreibung und Anwendung eines mathematischen Instruments für die Mechaniker, und unmittelbaren Vergleichung der Circulbogen", in Bull. of Sci. Acad. Berlin, 1795.