Complex optical voodoo is for automatic leveling compensation: you need very accurate vertical "zero" and 2 bubble levels aren't good enough. Fluid will make "contour" and optoelectronics shall read the amount of correction with 1" arc precision. Angle measurements are complex. The fixed part shall read simultaneously from the opposite side of the disk to reduce concentric errors. "Flying" disk compensates for the graduation error. T2000 was a high precision instrument from a 100 years old company. T1000(!) was a "simpler" model introduced in 1985.

In case you didn't know, the fluid inside the thing at 38:24 is ethylene glycol, it's used in a bunch of different optical things. It's not volatile but it is pretty toxic so y'know, be careful and stuff. And yes, I realise I'm like six months late telling you this haha.

I remember back in the mid to late 80's I worked for a company than designed Hand Held computers. One of the things that they were used for was collecting data from theodolites. (The interface wasn't serial RS232, but something more akin to SPI by the way). I remember having to solve a problem with the interface, so had access to the theodolite which was similar to this one, but with the distancing attachment. I reckon that the oil filled optical device, is all to do with the electronic levelling. I seem to remember that there was a calibration process to go through. The theodolite was initially levelled the old fashioned way using the spirit levels. As part of the calibration you would then sight the theodolite to a prism. The theodolite was then rotated 180 degrees and the telescope flipped 180 degrees (hence the reason for the handle to be moved out of the way). You would then re-sight the prism. In effect you have delta calibrated the instrument, thus eliminating any errors in the manual levelling.

I guess you figured out what the fluid was for, but if not: It's the level compensator. If the unit is slightly out of level, the fluid slants, and the optical path is reflected off of the surface of the fluid from underneath, and if the liquid surface changes angle it changes the optical path slightly thus compensating for slight tilt in the instrument.

I always wanted to take one of those apart !

This was an interesting teardown, and ticked all the boxes... *Retro (80s) tech. *Old-skool MCUs and PROMs. *Precision mechanics and optics *Lots of bolts to take out. *Something most people wouldn't normally get to see. *Oil. lol I genuinely predicted the oil to leak out, as I couldn't think of what else would be in there. lol I thought it was maybe just a prism at first, but it seemed too hermetically sealed for that. Reminds me a bit of the oil-filled lenses on the old CRT-based rear-projection TVs.

Very interesting, & a great piece of engineering. Thanks Mark 👍

Amazingly interesting insides. Really didn’t expect that.

38:25 Ha! WTF? Optical fluid? These instruments are quite ingenious.

The non electronic ones have to have about the same optical paths, just without the overkill, as the electronic one is meant to be accurate to the centimeter level over a kilometer, so you need to have a very accurate reading of both azimuth and attitude, to get that sort of precision. You typically start off at a datum point on your plot, and then go along with a path that leads you back to the origin again, so that at the end, when you have completed it, you can have an idea as to the overall error in your measurement, as the angles and distances measured should come back, after doing the math, or having a computer do it in this case with the unit, to be within your error budget for the path. If not, you have made a mistake somewhere, and simply have to redo the survey, so that the final error is negligible, giving confidence in the survey result. Part of surveying, making sure that you have not had a systematic bias, wrong data taken down, wrong measuring or equipment failure along the way. The newer versions of this now also come with a GPS receiver in them, along with a separate radio receiver, that is used with a known located GPS receiver that is broadcasting the difference in position of it's location, so that your theodolite can have it's location mapped down to miilimeter accuracy on the site, as a further check of the data. GPS might only be accurate within a meter, but differential use can easily get better, especially since the more modern receivers sample at the baseband frequency, instead of downconverting to 70MHz like the original ones, and can measure time to picoseconds, even with SA turned on. Provided both can see the same constellation they will remain in lock, giving you a very accurate position relative to the stationary unit, even if it's indicated position is varying by meters with time.

Oil maybe mechanical vibration damping and/or to get a particular refractive index

Most overkill use for one, setting a gate rail. We padded it to be within 1mm of level all the way through the travel, mostly because my brother in law is a civil engineer, and had it with him for work, so was the perfect tool to use for the job. Was actually quicker than using a spirit level, and was also much more accurate. Didn't even have to extend the yardstick either, top was at the right height for the job.

@09:21 there's a sticker showing the date it was checked - 26 June 1986

I am watching this video again because I did just order a Pentax PTS-II 05, more modern instrument and with built-in telemeter !

Skip to 7:30 for the actual tear down. I've never seen such a thing from the inside either.

Good explanation

38:24 Release the schmoo!

Cool, always did wonder what was in one of these things. Now I know :D Thanks

i have seen that solder mask material before, but i have never seen such a strange crossing trace layout like that

Really advanced device for the time

Thanks a lot, I always wonder how these are working, I was expecting some high precision encoders but not quite this.. I never saw some fluid optics except for that focusing water "droplet", this is indeed some optics voodoo :D I can only guess that the refraction index of that oil is very important and maybe the same as the glass for some funky optical behavior ;)

Thank you so much. I have problem That the lower plate can not levelled. Because 2 Rollers not moved

Enjoyed that thanks :)

always wondered what was in one of them.

I'm looking for a T 2002 Wild Total Station

Maybe the fluid stuff is a gravity vector detector (A.K.A. a level.) : ) A bubble may have been involved, but you let it get away. I see level indicators on the base, but they're probably just to get you close.

10:19 That mini screwdriver and bit set looked ace. Mind if I ask where you got it?

Nice opening titles :-)

15:53 - That is super weird PCB... 38:40 - Interesting, they are using some kind of oil with optics, for what reason? To keep things cool, lubrication or to change the optical characteristics? We'd never know... This is the most advanced craziest optical device I have ever seen, makes no sense lol

could the fluid chamber be for thermal compensation?

Are you going put it back together?

I have a T2002 that needs servicing you interested?

friend I am a young student I have a gps leica 530 I beg you to help me with a copy of ski pro 2.5 or earlier and with a copy of the gps530 emulator I live in Nicaragua thanks friend.

More like Wild Heerbrugg T2000 Theodolite destruction....

Wild... That sounds disgusting. Read the company name correct. Pronounce in German, not English!!! Hah... Try mount it back and it will not function. All you did - destroyed this rare high-precision instrument. It lost all value as museum piece.

Dude, the ads in the middle of the video are lame. You have a job, right?