This Askania Tu400 theodolite was part of a large donation to my collection together with a 1962 Wild T2, a 1969 Wild T2E theodolite, a 1951 Wild N2 level, a 1960s Jenoptik Koni 007 level, a 1960s Zeiss Opton Ni 2 level, a 1956 geodetic sextant, and various accessories.

The above mentioned group of instruments once was part of the set of instruments used by the field organisation TGTW of the Survey Department (Meetkundige Dienst, 'MD' in short) of Rijkswaterstaat (part of the Dutch Ministry of Infrastructure and the Environment, responsible for the design, construction, management and maintenance of the main infrastructure facilities in the Netherlands).

The registration number "AS1" (see figure 15) indicates that this was the first (and perhaps only?) Askania Tu400 bought by that department.

The field organisation TGTW was closed in the early 2000s and in 2008 the instruments were donated to my collection.

The Tu40 is an instrument with glass circles and an optical reading mechanism, clearly influenced by the instruments of Heinrich Wild like the ThI he developed for Carl Zeiss and the archetype T2 he developed later within his own firm.

The link with Carl Zeiss is obvious as the base of instruments like the Carl Zeiss Th42 is interchangeable with the Askania tribrach thanks to their DIN 18719 stub and socket joint (see figure 13 and figure 14). The carrying dome shows similarities to the ones used by Wild Heerbrugg (see figure 4), although the one from Askania is considerably wider at 190mm outer diameter (measured halfway up the dome).

The Tu400 was first advertised in the Netherlands at the end of 1956 as the "Theodolieten Model 1956" (earlier advertisements only show levels and non-automatic theodolites). It could be ordered with an astronomical (inverted view) or geodetic (erect view) telescope and with either sexagesimal or centesimal divided circles.¹

According to the 1956 advertisement it could be read to a single arc second or 0.0002 gon and estimated one digit further. The 1957 Askania brochure listed the Tu400 as an instrument for triangulation, traversing and field astronomy (see figure 17).² In 1967 a degree version of the the Askania Tu400 was listed as the K&E KE-2(e) 'One-Second Theodolite' in the Keuffel and Esser catalogue (see figure 18).² That both instruments are the same is confirmed by Deumlich in his Instrumentenkunde der Vermessungstechniek (1972), p. 134.

On the instrument in my collection both the 90mm horizontal and 70mm vertical circles are divided in gon (400 divisions in a full circle) and - as indicated in the catalogue and brochure - can be read down to 0.0002gon (about 1 arc second, see figure 10) and estimated one further decimal. The instrument has a pendulum type compensator for the vertical circle (see figure 19).