U.S. Patent Specifications

In a device of the character described, the combination of an instrument unit, an aerial camera, sighting elements on the instrument unit selectively adjustable by the operator to sight a selected target, level elements on the instrument unit variable in accordance with the flight conditions, a plurality of means for indicating to the operator the positions of said elements, replicas of said indicating means, non‐accessible to the operator and means for projecting pictures of said replicas into the aerial camera, whereby the latter is adapted to photograph simultaneously the ground areas over which the aeroplane flies and the relative positions of the said elements.