\documentclass[twoside]{article}%

\setlength{\headheight}{12pt}
\setlength{\headsep}{10pt}

\usepackage{gcheck}
\usepackage[left=1in,top=1in, width=5in, asymmetric]{geometry}
\geometry{bindingoffset=20pt}
\geometry{showframe,dvips}

\begin{document}

\typeout{}
\dcheck\paperwidth{8.5in}
\dcheck\paperheight{11in}
\dcheck\textwidth{361.34999pt}
\dcheck\textheight{614.29501pt}
\dcheck\oddsidemargin{20pt}% because of 'bindingoffset=20pt'
\dcheck\evensidemargin{0pt}
\dcheck\topmargin{-10pt-12pt}
\dcheck\headheight{12.0pt}
\dcheck\headsep{10pt}
\dcheck\footskip{30pt}
\dcheck\marginparwidth{121.0pt}
\dcheck\marginparsep{11.0pt}
\dcheck\columnsep{10pt}
\dcheck\hoffset{0pt}
\dcheck\voffset{0pt}
\ccheck\mag{1000}
\checkresults
\typeout{}

\manyfoxes\manyfoxes\manyfoxes\manyfoxes
\manyfoxes\manyfoxes\manyfoxes\manyfoxes
\manyfoxes\manyfoxes\manyfoxes\manyfoxes
\end{document}