I've used a 30 minute vernier, a 20 minute vernier, but never a 15 minute vernier.?ÿ
Here is a link to a 15' one.
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F323887845975
It makes me wonder. Did anybody make a 10' vernier?
These old instruments are a part of the genre of forgotten survey devices, I'm afraid. Along with drafting machines, planimeters, and (cough) pencils!
It seems to me that this trend is a one-way trend. We ain't goin back to them, and I have no desire to.?ÿ
Ah! Nostalgia! It's a sentimental thing.
Nate
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It makes me wonder. Did anybody make a 10' vernier?
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I'm pretty sure I've used a Nikon transit with a 10" vernier around 1980.?ÿ Probably manufactured right after WWII, it was an oldie.?ÿ It seemed to be a knock-off of a Leitz BT-20 but instead of gray hammertone it was a brown hammertone.?ÿ I remember thinking the 10" vernier would be more precise than the 30" K&Es and 20" Gurleys we were using, but the vernier was difficult to read.?ÿ This lead to a lot of blunders when attempting to read the circle.
With a clean 30" direct reading vernier it is possible to interpolate to 15" and less when the grooves were polished to your liking.
I cleaned and applied paste black boot polish to the verniers of a Dietzen on an as-needed basis. the other Iman liked nothing on the surface. We worked rain or shine in all environments. Construction projects and other barren soil laden areas required the most cleaning.
If we had to send an instrument into a shop we had to use a crusty ole K&E Paragon he had toted back and forth across Texas running some of the original electric transmission lines. The boss would not allow anyone to attempt to clean or open a cap.
Certain lots of instruments were superb and others were ok and all passed the same tests.
The vernier was an interchangeable and adjustable part with few special order spare parts to have picked from and they were short in supply.
0.02
Sorry to poop on anyone's parade, but early vernier geodetic transits were optically readable to 15" and if used in a stable environment by using a "winding up" technique could be good to less than 5". Kern & Wild T-2s, etc., with optical microscopes viewing both sides of a glass?ÿ plate simultaneously eliminated most plate errors, and micrometer coincidence adjustments were highly accurate for sub minute estimation, maybe good to 2-3 seconds with inversion techniques, again, within?ÿ environment and stable platforms, when observing distant targets.
Modern robots approach such accuracy; the limit is atmospheric considerations, target acuity and instrument stability.?ÿ I assert the T-2/T/3 type optical?ÿ instruments and larger pure optical instruments?ÿ are more accurate in angle determinations?ÿ than modern robots, with their prism target inaccuracies.?ÿ Let's not boast about our robot's angular accuracy when observing 1,000' or shorter foot shots.
Of course, GPS is much more accurate in the 30,000+ foot shot arena, where angles are less important than distance and the game devolves into +- a few tenths of?ÿ foot, good enough,?ÿ But if you're staking 2,000 feet of curb, a simple optical theodolite?ÿ will perform to +- 0.02', GPS?ÿ observations be damned,?ÿ
In good light, and with my 19-20 year old eyes, plus the magnifier on my Swiss Army knife, I could read our 30" Dietzen to 7.5". Nonadjustable legs, Keel (Lumber Crayon), 200' steel tape with the ring and leather strap on the end, plumb bobs, and Collins machetes: Those were the days!
@Mike Marks
I have many more hours behind a transit, than a T-2. But, I've got hours behind both.
The T-2 is much better. But we are not trying to mess anybody up. We are surveyors. We use the tools we've got.
N
