What is/was float option n? Unknown float option `n'

Question

I have an old LaTeX document (2005) that I want to compile. Latex complains that

! LaTeX Error: Unknown float option `n'.

These are all typical figures, like

\begin{figure}[n]
\includegraphics[width=0.9\textwidth,angle=270]{ngc121.eps}
\caption{NGC121}
\label{fig:ngc121}
\end{figure}

Note that all figures are eps files; I recall this file was originally compiled to dvi, and then converted to ps and pdf. My current latex says that it is pdfTeX 3.14159265-2.6-1.40.20 (TeX Live 2019/Debian), so there is obviously a version mismatch.

The amount of n and !ht figures in the document are about equal, so I assume the n was intentional and that this once worked.

Side note: I don't know why all the figures are rotated.

Before replacing the ns with other options, I'd like to know what the option was supposed to do so I can maybe mimic it. The n is not listed in e.g. https://en.wikibooks.org/wiki/LaTeX/Floats,_Figures_and_Captions

Answer 1

n has never been defined by LaTeX or common packages.

Prior to 2014, LaTeX did not give an error message for undeclared float options so [n] would have the effect of not allowing h, t, b or p so forcing the float to the end of the document unless flushed by \clearpage as it has no legal placement.

Since 2014 LaTeX gives an error for undefined placement option so [n] will raise an error.