In May 2019 I received my first HP 3810A. That example had been through the wars and was in a terrible state. All plastic components (covers, instrument panel, knobs, ocular) were broken and so was the internal cast-metal frame. In addition most parts of the yoke were heavily corroded and the battery-compartment and box were missing.

Still I was happy to receive it as this instrument was the very first to bear the name "Total Station" (see figure 7), a term now commonly used for any geodetic instrument capable of measuring distances, reducing them to horizontal or vertical and storing these values together with the corresponding vertical and horizontal angles in memory.

Sadly enough this first example was that terrible state that I did not want to display it. This all changed in June 2020 when another HP 3810A surfaced on a Dutch online marketplace. That one was in much better state, most likely as it had always been stored in its original case (see figure 13). It also was slightly older (ser.no. 733 vs. 1159), but as a result of that it lacked the text "Total Station" on the front. Luckily that front section was the only part of the first one that I found to have survived its rough treatment. So I dismantled the broken one, took off the front plate (and a few other parts that survived) and mounted the front plate on the older version, while keeping the original one.

The HP 3810A was not yet a Total Station in the sense of its modern successors like the 1980 Wild TC1 and the 1999 Leica TCRA 1101. Although it "... measures slope distance, zenith angle, corrects for curvature and refraction, and computes and displays horizontal or vertical distance", there was no internal storage yet, nor was there a way to read the horizontal circle electronically (that would first be achieved in 1977 in their model HP 3820A¹).

The HP 3810A was introduced in November 1975² and has been produced until at least 1981³. It was based on their HP 3800A Distance Meter which was introduced in April 1970.⁴

Most likely the concentric lens of the EDM influenced Wild-Heerbrugg in their design of the TC1, the first total station to look and measure along the same optical axis.

The HP 3810A was originally constructed with an internal telescope. The battered one that I found still had this telescope, although the eyepiece is missing its original collar. The second one, which is shown here, had the original internal telescope replaced by an external and most likely more powerful one. The bracket for this external telescope is still present, but the scope itself sadly enough is missing. The internal telescope was taken out and replaced by a counterweight to balance out the new scope. I therefore kept all the parts of the original scope of the battered one in the hope that one day I can revert this HP 3810A to its original scope.

The HP 3810A had a range of 1.6 kilometres using a set of three prisms.⁵ Its accuracy was stated as 5 millimetres + 5 millimetres per kilometre for a temperature range of -10°C to +40°C. It could do these measurements in single distance measuring mode or in tracking mode. In the mode the distance would be displayed in 3 decimal metres, otherwise in 1 decimal.

The horizontal circle could be read directly to 50 deci-milligon (20 arc-seconds) and estimated down to 10 deci-milligon (5 arc-seconds). The zenith angle was measured with an accuracy of about 90 deci-milligon or 30 arc-seconds.

With 12.1kg the instrument hardly was a light-weight instrument, while its dimensions of 345 x 360 x 325 millimetres makes it a substantial piece.