What is the affiliation of an industry author that works for a consulting company? If I am correct, (co)authors from industry are mentioned with their current employer as compared to PhD students that mention their university.
I know a case of an engineer that just started working in a certain company, as consultant of an external consulting company. He is (co)author of a paper based on his thesis. I wondered what he should mention on the paper:


His university. He wrote the thesis itself as a student, but is currently no longer working there.
The consulting company. This is his official employer, but has no link with his daily job as to its content.
The company in which he works. No, because it is not his official employer.
Both the consulting company as the company in which he works.
Nothing. Is this possible?
He should just use his official employer.  There are lots of scientific papers from people with affiliations in industry.  Most of the time, these authors are working for companies in technical fields that are at least somewhat related to the research, but not always.  (I knew of somebody who was still working with his doctoral advisor doing research in theoretical particle physics, while he was employed at a company making speech recognition software, and the software company was his listed affiliation.)  Especially if most of the other authors have more conventional affiliations, listing a consulting company for one authors is not going to raise any eyebrows.

If the manuscript was completely written while he was a student, he could use his university affiliation, with a footnote indicating his current position.  However, I would imagine in this case that the text was not finalized until after the author moved into industry, in which case the university affiliation is not appropriate.