The theodolite is the basic measurement instrument used in land surveying and construction. It allows measuring distances between points in the field based on angles measured and trigonometric calculations performed. The main parts of a theodolite are the base plate (for mounting on a tripod), limbus (circle plate) and the alidade, i.e. the turning part, which includes the scope, among other parts. The presented repetitive (bi-axial) theodolite in the field in reference to geographic directions. The instrument was made in the Fabryka Instrumentów Geodezyjnych Gustawa Gerlacha in Warsaw in 1938 or a little earlier. The establishment operated from 1816 to the World War II, and it specialised in producing land surveying instruments such as the theodolites, levellers, rangefinders, steel squares, and topographic tables. The company also produced other, small accessories for land surveyors. Instruments from the G. Gerlach factory were considered to be on par in terms of quality with products of the most renowned German manufacturers, such as Zeiss. The company’s strong position was evidenced by international awards and the presence of its branch offices and sales outlets in several cities.
The presented unit was purchased by a Gdańsk land surveyor in G. Gerlach’s company sales outlet in Warsaw in 1938, and it was used in accordance with its purpose for more than a decade.

References:
M. Kluza, Polscy wytwórcy instrumentów naukowych w XIX wieku [w:] Polscy twórcy aparatury naukowej, red. A. Strzałkowski, Monografie series, vol. X, Kraków 2006, pp. 277–285.
G. Gerlach najstarsza polska wytwórnia sprzętu geodezyjnego, prepared by S. Walczak, exhibition catalogue of the Museum of Technology in Warsaw in accordance with the programme prepared by the Main Commission for Museums and Exhibitions of the Polish Surveyors’ Association, Warsaw, October 1973.