This vintage Keuffel & Esser slide ruler, manufactured in the United States in the 1950s, measures 13 inches and comes with a manual. It is a collectible item related to science, medicine, and engineering, specifically in the category of slide rules.

This could be from late 1940s, however I know my dad was using it in the 50s as an engineering student.  There is a small Crack in the glass window on one side,  and the glass is missing on the other.  See photos.

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