Title: Device such as an instrument for optically, preferably visually, determining a definite plane

Abstract: A parallelepiped box is provided with three screens of parallel opaque lines, forming a definite plane, separated by transparent interspaces, and with a mirror behind the screens to direct ambient light from an opening in the top of the box through the screens. A forward screen is provided in the front of the box. Two rearward screens are behind the forward screen with one screen at an angle with the forward screen, the angle being in the definite plane formed by the parallel lines. Light enters the box through a diffuser in the opening and is directed through the screens to produce moire patterns indicating whether an observation is made above, below or in the definite plane. A second mirror may be provided above the opening to direct ambient light thereinto or a light source may be located above the opening to provide light thereto.

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Inventors: Bergkvist, Lars A. (890 42 Mellansel, SE)

Application Number: 946388
Filing Date: 1978-09-27
Publication_date: 1981-01-20
Assignee:
Primary Class(es): 356/618 356/399
Other Classes:
US Patent Ref:

3604813

Sep, 1971

Te Kronnie et al.

356/374.

Other Refs:
Primary Examiner: McGraw, Vincent P.
Assistant Examiner: Bovernick, Rodney B.
Attorney: Silverman, Cass & Singer, Ltd.