# How to change the default value bond length to an absolute value in chemfig?

Chemfig allows you to set bond length in the second argument of the bond, like -[,2] (a multiple of 2 to the default value). How to set the value of bond length for an absolute value (like 5mm), instead of a multiple of the default value?

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You can:

\documentclass{article}
\usepackage{chemfig}
\makeatletter
\newcommand*\forcelen[1]{#1/\CF@atom@sep}
\makeatother
\begin{document}
These bonds are exactly 5mm long: \chemfig{-[,\forcelen{5mm}]-[:60,\forcelen{5mm}]}
\end{document}


If both atoms are not empty, the argument of \forcelen is not the length of the bond. It is the distance between the centers of the atoms.

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It works great! I would like to know if it is able to make the setting globally, so that all the bonds drawn in the document has the specified bond length (like 5mm) instead of using the optional argument every time. –  bingung Dec 31 '13 at 12:03