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United States of America Patent
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Dec 16, 1986
Grant Date -
N/A
app pub date -
May 3, 1983
filing date -
Sep 16, 1981
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A device for indicating a definite direction, comprising a screen located in front and a screen located behind, which comprise opaque lines (3) separated by transparent interstices (4), whereby a moire pattern arises when the device is viewed. The screens (8,9) have different division. The opaque lines (3) have the same width in both screens (8,9). According to the invention the device is characterized in that one of the screens (9) is provided with only one opaque line less than the other of the screens (8), that in said one screen the width of a transparent interstice plus the width of an opaque line (3) is greater than or about equal to 1.5 times the width of the opaque line, but smaller than 1.9 times said width, preferably 1.5 times to 1.8 times the width of the opaque line. The two screens, further, are positioned symmetrically in relation to each other so that a central opaque line of one of the screens symmetrically overlaps a central transparent interstice of the other screen. Hereby a moire pattern with only one, relatively narrow interference strip is obtained, which is placed symmetrically over the screen surface.
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