Place a ruler somewhere on a page

Maybe package layout will help. It provides the command \layout which inserts one (onesided document) or two (twosided documents) pages that show the relevant sizes of the current page layout.

\documentclass{book}
\usepackage{geometry}% needed if the format of the document differs from the settings of your TeX system
\usepackage{layout}
\begin{document}
  \layout
\end{document}

Odd page:

enter image description here

Even page:

enter image description here


Or you can use package scrlayer. Then you can define a new page style using a layer with contents=\layercontentsmeasure.

\documentclass[a4paper]{book}
%\usepackage{geometry}
\usepackage{blindtext}

\usepackage{scrlayer}
\DeclareNewLayer[
  foreground,
  innermargin,
  contents=\layercontentsmeasure
]{measurelayer}
\DeclareNewPageStyleByLayers{measurestyle}{measurelayer}

\begin{document}
\chapter{A Chapter}
\Blindtext
\pagestyle{measurestyle}
\clearpage
\Blindtext
\clearpage
\pagestyle{headings}
\blinddocument
\clearpage
\end{document}

enter image description here

There are other predefined layer areas like topmargin, head, headsep, textarea,... But you can also define the size and the position of a layer:

\DeclareNewLayer[
  foreground,
  hoffset=1cm,
  voffset=.5cm,
  width=2cm,
  height=10cm,
  contents=\layercontentsmeasure
]{measurelayer}

enter image description here

Or you can modify a predefined layer area:

\DeclareNewLayer[
  foreground,
  topmargin,
  addheight=\dimexpr\headheight+\headsep\relax,
  contents=\layercontentsmeasure
]{measurelayer}

enter image description here


Instead of a ruler you could put a grid behind the text with eso-pic package:

\documentclass{article}
\usepackage[grid,
  gridcolor=red!20,
  subgridcolor=green!20,
  gridunit=in]{eso-pic}
\usepackage{lipsum}

\begin{document}
\lipsum 
\end{document}

enter image description here


There is a new package for this aim, namely fgruler:

http://www.ctan.org/pkg/fgruler

For example, try the following simple code:

\documentclass{article}
\usepackage[type=none]{fgruler}
\begin{document}
\fgruler{upperleft}{1cm}{2cm}
text
\ruler{rightup}{3cm}
text
\end{document}

enter image description here