[texhax] measurements using mathematical operations

[Martin Schröder]

2011/12/16 Demyan Prokopchuk <dprokopchuk at gmail.com>:
> Is there a way to define a measurement relative to another using simple mathematical operations? For example, if I wanted a horizontal line that was one inch shorter than \textwidth?
>
> % something like this
>  \rule{\textwidth-1in}{0.2mm}

\usepackage{calc}

Best
   Martin