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TeX stores dimensions internally in scaled points but operation \the expands to the corresponding value in points. Can we avoid the conversion and get the more precise, "original" value instead?

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$ tex \\relax
This is TeX, Version 3.14159265 (TeX Live 2014) (preloaded format=tex)

*
(Please type a command or say `\end')
*\dimen0=3.5in

*\showthe\dimen0
> 252.94499pt.
<*> \showthe\dimen0

? 

*\count0=\dimen0

*\showthe\count0
> 16577003.
<*> \showthe\count0

dimen values are just integer values interpreted as sp so you can do the above (although actually there is no loss of precision I think in the fractional pt value tex shows, it always shows enough decimal places to determine the exact value in sp)

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  • 2
    If e-TeX is available, \showtokens\expandafter{\number\dimen0} avoids assigning the value to a count register. In general \number\dimen0 will expand the dimension in scaled points (with possible number termination problems, of course). – egreg Oct 23 '14 at 8:58
  • This was an easy question :-) But how about dimension values in the output file? Can we have them in scaled points, too? – SJU Oct 23 '14 at 11:45
  • @egreg What are number termination problems? – SJU Oct 23 '14 at 11:47
  • @AngelTsankov Don't worry: leave a space after \dimen0 and you'll be OK. – egreg Oct 23 '14 at 11:53
  • @egreg so modern, as always, I forget the 1980's have finished. – David Carlisle Oct 23 '14 at 11:57
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For printing a length in sp units, define

\newcommand\lengthinsp[1]{\number\dimexpr#1\relax sp}

This will accept \lengthinsp{\parindent} (with a register) or even \lengthinsp{3.5in}.

Example:

\documentclass{article}

\newcommand\lengthinsp[1]{\number\dimexpr#1\relax sp}

\begin{document}

\lengthinsp{\parindent}

\lengthinsp{3.5in}

\end{document}

enter image description here

This is fully expandable. If you don't want to depend on e-TeX, a non-expandable version is needed:

\makeatletter
\newcommand{\lengthinsp}[1]{%
  \begingroup
  \dimen@=#1\relax
  \number\dimen@ sp%
  \endgroup
}
\makeatother
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