Ertel and Sohn
Information from The Planimetrica Collection website: Traugott Leberecht von Ertel (1778-1858). In 1806 he worked for Reichenbach, Utzschneider, und Liebherr (est. 1804, geodetic instruments), and left with Reichenbach. T. Ertel & Sohn established in 1821. 1850 address, Karls Strasse, Munich, near to G & S Merz, also established by Reichenbach. Sons: Georg Ertel (1813-1863); Gustav Ertel (1829-1875). In 1890, Diez purchased Ertel, and used the name T. Ertel & Sohn. In 1911, Julius Rinnebach joined the firm. By 1983, Ertel were specializing in theodolites.
Various Ertel & Sohn instruments are on display at the Deutsches Museum.
Sources of Information
-  The Planimetrica Collection: Ertel & Sohn (fl. 1821- ca.1985), München