In section 3 it contains a description of the VLBI technique used by the Event Horizon Telescope and the algorithms used to process the data. The methods rely on deconvolution[2] which behave nicely when dealing with pure signals, but can be tricky in practice on noisy data.
[1]: https://academic.oup.com/mnras/article/534/4/3237/7660988
I find it curious that they would try to image something that hasn't been observed by telescopes, and where we don't even know it's true appearance, without first proving that the method would work for something we already know, to act as a reference.
It can be seen from Table 1 and Figure 4 that the inner jet structure determined by 1.3 mm VLBI agrees well with the reported inner jet orientation at lower frequencies (e.g., Shen et al. 2002)
and from the conclusions:
For the first time, an AGN jet is spatially resolved with 1.3 mm VLBI with robust closure phase measurements. At pc scales, the inner jet direction is oriented toward the northwest (P.A.= −53◦) with respect to the assumed core, consistent with previous results.
The paper from 2002 can be found here[3].
edit: Also do note that the EHT is kind of a "virtual" telescope. It's using existing radio telescopes[4] to collect data, and these telescopes have been built and used for other stuff and so are well characterized.
[1]: https://en.wikipedia.org/wiki/Event_Horizon_Telescope#J1924-...
[2]: https://arxiv.org/abs/1208.4402
Anyone know the expected timeline for better data?
Is there any other milky way in the universe?
I'm not saying there's never a use for it, but only in areas with established information to see how it will develop (a weather forecast is a great example), it should never be used to generate the information (i.e. fill in gaps in experimentation or observation).
