# Placeholder number with siunitx

I would like to add a placeholder number in my text, to remind me that I still have to look it up, later. I usually just use something like "XYZ" or "???" for this. But when I'm using the \SI notation I get an error that "?" is not a number.

\documentclass{article}
\usepackage{siunitx}

\begin{document}
I don't know yet what number to place here: \SI{???}{\percent}.
\end{document}


The error I get is:

siunitx error: "invalid-token-in-number" Invalid token '?' in numerical input. For immediate help type H <return>. ...at number to place here: \SI{???}{\percent}


What is the best/suggested way to add a placeholder number or symbol in SI-notation?

• My welcome into the site of TeX.SE. – Sebastiano Mar 28 '19 at 22:04

You can pretend that ? is a valid input 'symbol' such as \pi.

\documentclass{article}
\usepackage{siunitx}
\sisetup{
input-symbols={?},
}

\begin{document}
I don't know yet what number to place here: \SI{???}{\percent}.
\end{document}


The same works for XYZ

\documentclass{article}
\usepackage{siunitx}
\sisetup{
input-symbols={XYZ},
}

\begin{document}
I don't know yet what number to place here: \SI{XYZ}{\percent}.
\end{document}


Alternatively, you could stop siunitx from parsing numbers. Either globally with \sisetup{parse-numbers=false} or locally with \SI[parse-numbers=false]{???}{\percent}.

• That works perfectly. Thanks for the quick answer! I'm curious, though. Can you explain why there is a small gap between the first and second character, when I use the 'input-symbols={?}' method? It looks something like "? ?? %" or "X YZ %". If I disable number parsing it looks as expected, like "??? %". – Vincent W. Mar 28 '19 at 22:03
• I have understood that the OP didn't know what to put in the place of the ??? – Sebastiano Mar 28 '19 at 22:03
• @VincentW. It seems that siunitx still groups the ? as if they were normal digits. In the MWE I get ?, ??, ???, ????, ??\,??? etc. pp. I do not get ?\,?? though... With parse-numbers=false that digit grouping does not happen. – moewe Mar 28 '19 at 22:08
• @moewe I get ?, ??, ?\,??, ?\,?\,??, ??\,?\,??. But regular 1234 when I use numbers. Strange... But also not really important. Maybe some language settings... – Vincent W. Mar 28 '19 at 22:17
• @VincentW. Would have been my guess as well, I didn't find anything in the docs on a quick read, though. Do you get that result with my MWE or in your larger document? – moewe Mar 28 '19 at 22:19