ORIGINAL PATENT APPLICATION NUMBER 289872 FOR IMPROVEMENTS IN THE METHOD AND APPARATUS FOR DETERMINING THE INSTANTANEOUS POSITION AND THE SPEED AND DIRECTION OF MOVEMENT OF INVISIBLE AIR CRAFT BY EXCLUSIVELY ACOUSTIC MEANS., (BRATISLAVA, CZECHO-SLOVAKIA).
(also known as Actiova Spolecnost Opticky Ustav). Aktiengesellschaft C. P. Goerz Optische Anstalt.