Theodolites are precisions instruments that measure angles. Using these measured angle and trigonometry, locations and elevations can be determined to a very high level of
accuracy. Theodolites are an important part of surveying used to map out the geographic and political boundaries. We have complete confidence in their accuracy because of the 200 years of successful usage.
See here for the background and history of theodolites: https://celebrating200years.noaa.gov/theodolites/welcome.html
Theodolites are the bane of flat earthers as the measurements from Theodolites directly measure the curvature of the earth totally discrediting the idea of a flat earth.
Flat earthers do not care about discovering truth but instead only care to support their bias so they must not allow measurements from theodolites. There are two common attempts to discredit and dismiss measurements from theodolites: they are not certified to be used over a specified distance and optical collimation errors.
I will address each one separately.
Claim: Theodolites are not certified to be used over a specified distance
I have asked flat earthers for citations on the manufacturer’s certified maximum distance but have not received any. If you know of any manufacturer’s documentation, please send to me: email@example.com
YouTuber The Maine Surveyer has provided some details on this topic.
Here’s a brief datasheet on the Leica TS16 total station that I use. Notice that the distance limitations are only on the distance measurements, not on the angles. The angle measurements are limited only to the operator’s ability to see the target and turn to it two or more times with reasonable accuracy.
Here is the operation manual on the TS16. In long range mode, it can shoot distances greater than 33,000 feet. (Page 70 of 90) Leica TS16 Total Station User Manual
To be purely technical, theodolites don’t shoot distances, they only measure horizontal and vertical angles (sometimes called zenith angles, depending on where 0 degrees is).
This gives some basic information on the Wild Heerbrugg T2 theodolite. Jesse Kozlowski owns one. Notice that the direct read accuracy is 1 second. Some models allow the user to estimate a half second. There is no distance limitation; again, the distance to the target is limited only by the operator’s ability to see it.
Here’s some information on the Wild T3, which Larry Scott has. https://celebrating200years.noaa.gov/theodolites/wild_t3.html
Here is a datasheet for a Nikon theodolite similar to the one roohif used in his video debunking JTolan Media 1. It has no distance limitation, since, like all theodolites, it has not on-board laser. It only measures angles.
For more information, see The Maine Surveyers YouTube channel.
Claim: Theodolites cannot be used because of collimation errors
This claim goes back to the writings of Samuel Rowbotham. He had made claims that the horizon always rose to eye level. Surveyors knew this was not the case and pointed this out to him. He then made up the excuse of collimation errors causing the apparent drop.
From Samuel’s book “Earth not a Globe”:
He ascertained that in those of the very best construction, and of the most perfect adjustment, there existed a certain degree of refraction, or, as it is called technically, “collimation,” or a slight divergence of the rays of light from the axis of the eye, on passing through the several glasses of the theodolite.
All measurements have errors. Collimation errors are a real thing for theodolites that can cause things to be measured slightly off. However, there is a process to correct for collimation errors.
The error can be eliminated by reading angles on both the faces and taking the mean of the observed values. See the links below addressing these types of errors and how operators of theodolites address the issues.
Acknowledging there are errors in measurements does not invalidate measurements. We need to track the amount of error that is possible in our instruments and include it in our calculations. If the size of the measurement is close to the margin of error, then the measurement cannot be used.
To suggest that a Theodolite cannot be used to measure the shape of the earth because of collimation is incorrect.
Below are some videos demonstrating how to test for collimation errors: