On May 21, 1878, Charles Vander Woerd patented a very interesting bimetallic balance, which was supposed to compensate for middle temperature error. Three horologists, Bandurski of Geneva, Adrien Philippe of Patek Philippe, and Charles Woerd, worked independently on the same idea, which was to introduce in the bimetallic lamina an arrangement that would cause the balance not to expand in a linear manner, as with the regular compensation balance. Since the irregularities caused by the changes inhe elasticity of the balance spring are quadratic, all three horologists tried to make the changes in the balance inertia quadratic as well. The idea was to change the way the forces of bimetallic expansion work; to accomplish this, they needed to change the contact surface between the lamina. All of them chose triangular contact. In Woerd's case, many watchmakers, when cleaning the watch, did not realize how fragile it was, and many were broken. The company replaced them with the highest Americn grade bimetallic balances, superbly polished and with beveled inner edges. The movements chosen to be employed with Woerd's balances were always of the highest standard.