Ertel-Werke München 637 Double Circle Repetition Theodolite Compass Wooden Case

Ertel-Werke München 637 Double Circle Repetition Theodolite Compass Wooden Case

The Ertel-Werke 637 is a Normal-Repetitions-Theodolith I — a double-circle repeating theodolite manufactured by Ertel-Werke A.G. of Munich, Germany. Repeating theodolites of this class allowed surveyors to accumulate multiple angle measurements on the horizontal circle and divide by the number of repetitions, achieving angular accuracy far beyond what a single reading could provide. This instrument carries serial number 32697 and is offered complete with its original wooden carrying case, surveying compass, and a full set of accessories.

Specifications & What's Included

Instrument type: Normal-Repetitions-Theodolith I (Catalog Nr. 637)
Serial number: 32697 (engraved on base plate)
Manufacturer: Ertel-Werke A.G., Barthstrasse 8, München, Germany
Telescope: Internal-focusing (Innen-Fokusier) design
Objective aperture: 23 mm
Objective focal length: 190 mm
Telescope magnification: 18×
Stadia constant K: 120 (fixed stadia wires)
Horizontal circle limbus diameter: 120 mm
Horizontal circle graduation: 1/3° (20-minute divisions)
Horizontal circle vernier reading: 30 arcseconds
Vertical circle limbus diameter: 100 mm
Vertical circle graduation: 1/3°
Vertical circle vernier reading: 30 arcseconds
Level sensitivity – horizontal circle alidade: 40 arcseconds per division
Level sensitivity – telescope carrier: 40 arcseconds per division
Level sensitivity – vertical circle alidade: 25 arcseconds per division
Reversion level (telescope): 20 arcseconds per division
Tribrach base with three leveling footscrews
Includes: detachable surveying compass (full 360° card, N/S/E/W, degree scale)
Includes: striding level with tubular vial
Includes: plumb bob with copper suspension cord
Includes: adjustment screwdriver, adjustment pins, and case keys
Includes: original dovetailed hardwood carrying case with brass hardware and carrying handle
Case interior: original Ertel-Werke specification label, accessory door holders, and instrument base board
Original catalog weight for this model with case: 11.1 kg (per manufacturer's original catalog sheet, visible in photos)

Applications

Repeating theodolites like the Ertel-Werke 637 were the standard precision angle-measuring instruments of land surveying, geodesy, and civil engineering from the late 19th century through the mid-20th century. The repeating (Repetitions) design was favored for triangulation surveys, boundary determination, and topographic mapping because it allowed accumulated angle readings — the surveyor would rotate the alidade multiple times around the circle, reading the accumulated arc and dividing, effectively multiplying precision without requiring finer graduation. Ertel-Werke A.G. of Munich was one of the leading German optical and precision instrument manufacturers of the era, producing theodolites, sextants, and astronomical instruments to a high standard; their instruments were used across Europe and exported worldwide. This class of instrument dates from the early-to-mid 20th century — the construction style, internal-focusing telescope, and circle-and-vernier reading system are characteristic of pre-WWII German precision manufacture. Today, instruments like this are sought by survey instrument collectors, museums, scientific instrument historians, and engineering schools as examples of classical geodetic craftsmanship. The compass attachment would have been used for magnetic azimuth orientation in the field, allowing the surveyor to establish a reference bearing before beginning angle traverses.

Condition: Used
This Ertel-Werke München 637 Double Circle Repetition Theodolite has been inspected and is in good condition for its age. It was pulled from a working environment where it was in active use. The instrument itself shows normal age-related patina on the metalwork — the black lacquered finish has light wear consistent with a precision instrument that has seen field use, and the white enamel tube and circle housing remains largely intact. The horizontal and vertical circles, verniers, and level vials are all present and intact. The telescope optics appear clear in the photos. The original dovetailed wooden case is structurally sound with typical wear to the exterior finish; the interior door retains the original Ertel-Werke spec label and accessory holders. Included accessories visible in the photos are the detachable surveying compass, a striding level, plumb bob with copper cord, adjustment screwdriver, adjustment pins, and case keys. Please view our photo set and contact us if you have any questions.

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Brand	Ertel-Werke
MPN	637

Ertel-Werke München 637 Double Circle Repetition Theodolite Compass Wooden Case

Specifications

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