Wild Heerbrugg “old style” N3 precision level in green enamel. Built-in parallel plate micrometer. Three screw leveling. Used for measuring vertical distances between points in conjunction with a levelling staff.
This “old style” N3 level was manufactured between 1940 and 1972. It was one of the most powerful levels of its time.
A description of this level and others can be found at http://www.dehilster.info/geodetic_instruments/1961_wild_heerbrugg_n3_level.php