Protective sleeve for microfilm card - has transparent window at each side for viewing microfilm card in sleeve

摘要

The sleeve has a rectangular aperture at either side, each being covered by a transparent film, so as to form two windows through which the microfilm card is visible. The latter carries a number of image frames of differing format, with the relatively rigid frame edges of the sleeve carrying line markings for denoting the positions of the various image frames. The line markings may be broken lines along two edges of the frame denoting the orthogonal coordinates of the respective image frame and/or may be of magnetic material to allow them to be read automatically to guide the objective of a microfilm viewer.