In January 2021 this total station came up for sale on a Dutch on-line auction. The Zeiss Elta 20 was developed by the West German branch of Carl Zeiss, Zeiss Oberkochen, in the late 1970s. Together with the Elta 2 the Elta 20 was the successor of the Elta 14, the first self-registering total station that was introduced in 1968. Whereas the Elta 14 was using a ticker-tape to store the observations the Elta 2 (of which the Elta 20 is a further development) was the first total station to use an internal memory device that was based on semi-conductor technology to store the observations.

The main differences between the Elta 2 and Elta 20 were the accuracy (see below) and the microcomputer, which was a swappable 12 program hub in the Elta 2 and a built-in micro-computer in the Elta 20.

The Elta 2 was first produced in 1978, followed by the Elta 20 and Elta 3 in 1981 and all three remained advertised together until at least 1983.¹ The Elta 2, Elta 20 and Elta 3 were housed in the same enclosure (see figure 15) and, apart from the type indication, all looked alike (with exception for the program module of the Elta 2) and used the same type of data storage.

The naming convention of Zeiss can create some confusion here. The Elta 3 mentioned here was a simplified version of the Elta 20 (see below), while in 1985 a new Elta 3 saw the light. That instrument, however, was built along completely new lines and does not resemble the older Elta 3, not visually, but also not technically. The same happened to the Elta 4 and even to the Elta 2. The instruments built after 1985 are significantly more modern and featured (among other changes) dual-axis compensators and LCD-displays. All these new models again look alike, but bear no resemblance to the old-style Elta 2, 3 and 4 (and 20) discussed here.

In the Elta 2 and Elta 20 angular readings are taken from the glass 98mm diameter horizontal circle at two diametrically opposite locations,² similar to what was done in optical theodolites since Heinrich Wild had introduced it in his 1924 Zeiss Th1. In the Elta 3 this is done at only one location.³

The Elta 20 is equipped with a single axis compensator, which is only used to correct vertical angles for tilt.⁴

The Elta 2 had two storage modules: the MEM200 and MEM400. The former had a capacity of 220 records, the latter 440 records.⁵ In or shortly before 1985, a few years after the introduction of the Elta 20, a third memory module, the MEM800, came onto the market with a capacity of 800 records.⁶ It is this memory module that came in twofold with this Elta 20 in my collection.

As the memory modules have an internal battery, I decided to open them to see their current status. One of the two modules had a date written on the battery (see figure 3), indicating that the instrument had been in use until at least 12 January 1989.

The arrival of data storage with the Elta 14, 2, 20 and their successors had an unexpected side-effect: surveyors called this way of data-acquisition 'blind surveying' as at the end of the day one only had a ticker-tape or memory module with data and no method to check the quality of that data. In order to overcome this issue each instrument had at the time a Volkswagen van with the necessary computer equipment (HP 85 and flat-bed plotter) to directly process the data.⁷

The person from whom I got the instrument from once got it from a former employee of the Dutch firm Grontmij. In October 1991 the land surveying department of Grontmij NV and the Dutch geodetic firm Bravenboer & Scheers Geodesie BV merged to form B&S Grontmij Geogroep,⁸ a sticker of which can be found on one of the battery cases of the Elta 20 (see figure 4). Above we have seen that the battery of one of the MEM800 memory modules was dated 1989 and thanks to this sticker and the Grontmij company history we can now safely state that the instrument has been in service until at least 1991.

The REC200 field book has its own set of three batteries and a accessory charger. Two of these batteries are adorned with a sticker as well (see figure 5), but this time not of a commercial party. Instead, these stickers show the text Rijksdienst voor de IJsselmeerpolders - Afdeling Landmeetkundig Werk (National Office for the IJsselmeerpolders - Land Surveying Department, see figure 5), indicating that at least these batteries once belonged to this Dutch governmental survey department.

This department, also shortened to RIJP, was founded on 29 March 1947 to centralise the cartographic activities.⁹ Initially they operated with six persons from the Dutch town of Zwolle with branches in Kampen and Emmeloord.

Their initial instrument of choice was the Wild T3, which was used to intersect beacons that were used to stake-out embankments. Up to at least 1957 points were also created using resection. Staking out the directions of the embankments themselves was done using a geodetic sextant.

In 1958 a Tellurometer was acquired for distance measurements to facilitate these activities. In the meanwhile the department became larger, employing 55 personnel by 1966.

In 1974 they started using Zeiss Reg Elta 14 total stations, which were replaced in 1981 with the more modern Zeiss total stations from the series discussed here. A picture in the article that is used as reference for this section shows an old-style Zeiss Elta 4, which could be used in combination with the REC100 field-book. This field-book did use the same batteries as the REC200 and the same memory modules as the Elta 20. The article was published in 1987 and does not mention the replacement of the Elta 4 by a more modern surveying instrument, but it seems that somewhere between 1987 and 1991 RIJP did modernise again and that B&S Grontmij acquired (some of) their instruments.